Ultrasound signal processing device, ultrasound diagnostic device

ABSTRACT

An ultrasound signal processing device: performing events involving transmitting ultrasound towards a subject; receiving ultrasound reflection from the subject in response to each event; and generating a frame signal from sub-frame signals generated based on the ultrasound reflection. The device, in each event, causes a transmission aperture to transmit ultrasound focusing in the subject. A transmission aperture for one event differs in position, in a transducer element array direction, from a transmission aperture for a previous event by a shift amount of at least twice a transducer element width. The device, for each event, sets a target area which includes a position where transmitted ultrasound focuses and whose width in the transducer element array direction, at a depth where the transmitted ultrasound focuses, is equal to or greater than the shift amount. The device generates a sub-frame signal covering measurement points included in the target area.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. application Ser. No.15/067,858, filed Mar. 11, 2016, which claimed the priority of JapanesePatent Application No. 2015-066483 filed on Mar. 27, 2015, bothapplications are incorporated by reference herein.

BACKGROUND OF THE INVENTION (1) Field of the Invention

The present disclosure is related to an ultrasound signal processingdevice, and an ultrasound diagnostic device equipped with the ultrasoundsignal processing device. In particular, the present disclosure relatesto receive beam forming in an ultrasound signal processing device.

(2) Description of the Related Art

Typically, an ultrasound diagnostic device transmits ultrasound towardsthe inside of a subject via an ultrasound probe (referred to in thefollowing as a “probe”), and receives reflected ultrasound (an echo) viathe probe. The reflected ultrasound is generated within the subject dueto tissues in the subject having different acoustic impedances. Further,an ultrasound diagnostic device generates an ultrasound tomographicimage based on electric signals acquired through the reception of thereflected ultrasound, and displays the ultrasound tomographic image on amonitor (referred to in the following as a “display unit”). Anultrasound tomographic image shows the structures of tissues inside thesubject. Ultrasound diagnostic devices are widely used for the imagingdiagnosis of subjects, for having low invasiveness and achievingreal-time observation of tissues through tomographic images and thelike.

A typical method applied in conventional ultrasound diagnostic devicesfor forming signals based on received reflected ultrasound (i.e.,receive beam forming) is delay-and-sum beam forming. One example ofdelay-and-sum beam forming can be found disclosed in pages 42-45 of“Ultrasound Diagnostic Device”, written by Masayasu Itou and TsuyoshiMochizuki and published by Corona Publishing Co., Ltd (Aug. 26, 2002).According to this method, transmission beam forming (i.e., transmissionof ultrasound by a plurality of transducer elements towards the insideof the subject) is typically performed such that a transmittedultrasound beam converges (focuses) at a predetermined focal depthinside the subject. Further, according to this method, measurementpoints are always set along the central axis of the transmittedultrasound beam, as illustrated in FIG. 27. Due to this, one ultrasoundtransmission event generates only one or a few acoustic line signalsalong the central axis of the transmitted ultrasound beam, and thus,reflected ultrasound is not utilized in an efficient manner. Inaddition, with this method, it is also problematic that an acoustic linesignal acquired from a measurement point distant from the transmissionfocal point has low resolution and low S/N ratio.

Meanwhile, a receive beam forming method is being proposed that utilizesa so-called synthetic aperture method to yield high quality images notonly from near the transmission focal point but also from areas otherthan near the transmission focal point. One example of receive beamforming utilizing the synthetic aperture method can be found disclosedin pages 395 through 405 of “Virtual Ultrasound Sources in HighResolution Ultrasound Imaging”, S. I. Nikolov and J. A. Jensen, in Proc,SPIE—Progress in Biomedical Optics and Imaging, Vol. 3, 2002. Accordingto this method, delaying is performed taking into consideration both apropagation path of ultrasound and the time amount required forreflected ultrasound to arrive at a transducer element by travellingalong the propagation path. Thus, the method achieves receive beamforming making use of not only reflected ultrasound from an area of anultrasound main irradiation area near the transmission focal point butalso reflected ultrasound from areas of the ultrasound main irradiationarea other than the area near the transmission focal point. Due to this,the method enables generating, from one ultrasound transmission event,acoustic line signals covering the entire ultrasound main irradiationarea, including areas far from the transmission focal point. Inaddition, the synthetic aperture method enables setting a virtualtransmission focal point based on multiple receive signals acquired foreach measurement point through multiple transmission sessions. Thus, thesynthetic aperture method enables acquiring an ultrasound image withhigher resolution and higher S/N ratio than the receive beam formingmethod disclosed in “Ultrasound Diagnostic Device”.

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

Meanwhile, in connection with the synthetic aperture method, research isbeing conducted to improve ultrasound image resolution per unit time, orthat is to increase ultrasound image frame rate. Considering constraintsrelated to the performance of ultrasound diagnostic devices, an increasein frame rate necessitates a reduction in the number of ultrasoundtransmission events. Meanwhile, with conventional transmission beamforming as described above, the wavefront of ultrasound converges asapproaching the transmission focal depth. Accordingly, a reduction inthe number of transmission events results in only some areas of thesubject along a direction in which ultrasound transducer elements arearrayed being irradiated with ultrasound, with areas not irradiated withultrasound existing therebetween, particularly at and around thetransmission focal depth. Conventionally, measurement points are not setwith respect to such areas not irradiated with ultrasound. Due to this,the areas not irradiated with ultrasound form blank areas in ultrasoundimages, i.e., defective areas in ultrasound images. Such defective areasmay lead to a prominent decrease in image quality of ultrasound images.

In view of such problems, the present disclosure provides an ultrasoundsignal processing device and an ultrasound diagnostic device equippedwith such an ultrasound signal processing device that achieve anincrease in frame rate, while suppressing the occurrence of defectiveareas in ultrasound images and the consequent decrease in image qualitythat would otherwise occur when combining the synthetic aperture methodwith conventional transmission beam forming.

Means for Solving the Problems

One aspect of the present disclosure is an ultrasound signal processingdevice: performing a plurality of transmission events each involvingselecting a first group of transducer elements from among a plurality oftransducer elements of a ultrasound probe that are arranged in at leastone line along a transducer element array direction, and causing eachtransducer element in the first group to transmit ultrasound towards asubject; for each of the transmission events, generating a sub-frameacoustic line signal based on ultrasound reflection received from thesubject in response to the transmission event, to yield a plurality ofsub-frame acoustic line signals each corresponding to a different one ofthe transmission events; and generating a frame acoustic line signalbased on the sub-frame acoustic line signals for the transmissionevents. The ultrasound signal processing device includes ultrasoundsignal processing circuitry that operates as: a transmitter that, ineach of the transmission events, selects the first group and causes eachtransducer element in the first group to transmit ultrasound focusing ata predetermined depth in the subject, the first group in onetransmission event differing in position, in the transducer elementarray direction, from the first group in a previous transmission eventby a shift amount corresponding to at least twice a width of a singletransducer element in the transducer element array direction; a receiverthat selects at least some transducer elements among the plurality oftransducer elements of the ultrasound probe, and generates a receivesignal sequence for each of the at least some transducer elements basedon ultrasound reflection received by the transducer element; adelay-and-sum calculator that, for each of the transmission events: setsa target area including a plurality of measurement points, the targetarea at least including an area where the ultrasound transmitted fromthe first group in the transmission event focuses in the subject,wherein at the predetermined depth, a width of the target area in thetransducer element array direction is equal to or greater than the shiftamount; and generates a sub-frame acoustic line signal composed of aplurality of acoustic line signals, one for each measurement pointincluded in the target area, by performing, for each measurement pointthat is included in the target area, delay-and-sum processing withrespect to one or more receive signal sequences corresponding to themeasurement point, the one or more receive signal sequencescorresponding to the measurement point respectively generated for one ormore transducer elements composing a second group of transducerelements, among the plurality of transducer elements of the ultrasoundprobe, based on ultrasound reflection received from the measurementpoint; and a synthesizer that generates a frame acoustic line signalbased on a plurality of sub-frame acoustic line signals correspondingone-to-one with the transmission events.

BRIEF DESCRIPTION OF THE DRAWINGS

These and the other objects, advantages and features of the inventionwill become apparent from the following description thereof taken inconjunction with the accompanying drawings which illustrate a specificembodiment of the invention.

FIG. 1 is a functional block diagram illustrating the structure of anultrasound diagnostic device 100 pertaining to embodiment 1;

FIG. 2 is a schematic illustrating a propagation path of ultrasoundtransmitted from a transmission beam former 103 pertaining to embodiment1;

FIG. 3 is a functional block diagram illustrating the structure of areceive beam former 104 pertaining to embodiment 1;

FIG. 4 is a functional block diagram illustrating the structure of adelay-and-sum calculator 1041 pertaining to embodiment 1;

FIG. 5 is a schematic illustrating a target area Bx pertaining toembodiment 1;

FIG. 6 is a schematic illustrating the relationship between atransmission aperture Tx and a receive aperture Rx set by a receiveaperture setter 1043 pertaining to embodiment 1;

FIG. 7A is a schematic pertaining to embodiment 1, illustrating onepropagation path of ultrasound that is transmitted from the transmissionaperture Tx and arrives at a receive transducer element Rk via ameasurement point Pij; FIG. 7B is a schematic pertaining to embodiment1, illustrating another propagation path of ultrasound that istransmitted from the transmission aperture Tx and arrives at a receivetransducer element Rk via a measurement point Pij;

FIG. 8 is a functional block diagram illustrating the structure of asynthesizer 1140 pertaining to embodiment 1;

FIG. 9 is a schematic illustrating processing by an adder 11401pertaining to embodiment 1 for generating a combined acoustic linesignal;

FIG. 10A is a schematic pertaining to embodiment 1, providing anoverview of maximum overlap counts for combined acoustic line signals,and FIG. 10B is a schematic pertaining to embodiment 1, providing anoverview of amplification by an amplifier 11402 that is based on themaximum overlap counts for the combined acoustic line signals;

FIG. 11 is a flowchart illustrating beam forming by the receive beamformer 104 pertaining to embodiment 1;

FIG. 12 is a flowchart illustrating operations of the receive beamformer 104 pertaining to embodiment 1 for generating an acoustic linesignal for a measurement point Pij;

FIG. 13 is a schematic for explaining the operations of the receive beamformer 104 pertaining to embodiment 1 for generating an acoustic linesignal for a measurement point Pij;

FIG. 14 is a schematic illustrating the relationship between atransmission aperture Tx and a receive aperture Rx set by a Tx receiveaperture setter pertaining to modification 1;

FIG. 15 is a flowchart illustrating beam forming by a receive beamformer of an ultrasound diagnostic device pertaining to modification 1;

FIG. 16 is a schematic for explaining the operations of the receive beamformer pertaining to modification 1 for generating an acoustic linesignal for a measurement point Pij;

FIG. 17 is a functional block diagram illustrating the structure of areceive beam former 104A of an ultrasound diagnostic device pertainingto embodiment 2;

FIG. 18 is a schematic illustrating a target area Bx pertaining toembodiment 2;

FIG. 19A is a schematic illustrating processing pertaining to embodiment2 of generating a primary combined acoustic line signal by combiningprimary sub-frame acoustic line signals, FIG. 19B is a schematicillustrating processing pertaining to embodiment 2 of generating asecondary combined acoustic line signal by combining secondary sub-frameacoustic line signals, and FIG. 19C is a schematic illustratingprocessing pertaining to embodiment 2 of generating a frame acousticline signal;

FIG. 20 is a flowchart illustrating beam forming by the receive beamformer 104A pertaining to embodiment 2;

FIG. 21A is a schematic pertaining to modification 2, illustrating onepropagation path of ultrasound, FIG. 21B is a schematic pertaining tomodification 2, illustrating another propagation path of ultrasound,FIG. 21C pertains to modification 2 and illustrates one example of arelationship between depths D of measurement points Pij and transmissiontimes for the measurement points, and FIG. 21D pertains to modification2 and illustrates another example of the relationship between depths Dof measurement points Pij and transmission times for the measurementpoints;

FIG. 22A is a schematic pertaining to modification 2, illustratingpropagation paths of ultrasound, FIG. 22B pertains to modification 2 andillustrates one example of the relationship between depths D ofmeasurement points Pij and transmission times for the measurementpoints, and FIG. 22C shows one example of an ultrasound image in which agap in luminance is observed at both sides of a focal depth, at areascorresponding to secondary sub-frame acoustic line signals;

FIG. 23A is a schematic pertaining to modification 3, illustratingpropagation paths of ultrasound, FIG. 23B pertains to modification 3 andillustrates one example of the relationship between depths D ofmeasurement points Pij and transmission times for the measurementpoints, FIG. 23C illustrates one example of a relationship betweenvariable α used in calculating transmission times and depths D ofmeasurement points Pij, and FIG. 23D shows one example of an ultrasoundimage in which a gap in luminance is observed at boundaries betweenareas corresponding to primary sub-frame acoustic line signals and areascorresponding to secondary sub-frame acoustic line signals;

FIG. 24A is a schematic illustrating a target area Bx pertaining tomodification 4, and FIG. 24B is a schematic illustrating processingpertaining to modification 4 for generating a frame acoustic line signalfrom frame part acoustic line signals;

FIG. 25A is a schematic illustrating one example of a target area Bxpertaining to another modification, and FIG. 25B is a schematicillustrating one example of a target area Bx pertaining to yet anothermodification;

Each of FIGS. 26A through 26D shows an example of an ultrasound image;

FIG. 27 is a schematic illustrating delay-and-sum processing in aconventional ultrasound diagnostic device; and

FIGS. 28A and 28B are schematics for explaining a problem arising whencombining conventional transmission beam forming causing wavefront toconverge, with the synthetic aperture method.

DESCRIPTION OF EMBODIMENTS How Inventor Arrived at Aspects of PresentDisclosure

The present inventor conducted much research for achieving increasingframe rate with an ultrasound diagnostic device employing the syntheticaperture method.

A conventional ultrasound diagnostic device performs transmission beamforming (i.e., transmission of ultrasound by a plurality of transducerelements towards the inside of the subject) by causing wavefront oftransmitted ultrasound to converge (focus) inside the subject at thetransmission focal depth. Thus, each transmission event results in aspecific area inside the subject receiving most of the reflectedultrasound (echo signals) from the transmission transducer elements,which are transducer elements used for ultrasound transmission.Specifically, this area, referred to in the following as an ultrasoundmain irradiation area, is an area including measurement points whereultrasound transmitted from all transmission transducer elements arein-phase. For example, when ultrasound transmission is performed withone measurement point set as the transmission focal point, theultrasound main irradiation area has an hourglass shape, the bottom edge(i.e., base) of the ultrasound main irradiation area corresponds to thearray of the transmission transducer elements, and two straight lineseach extending from a different end of the base towards the transmissionfocal point partition the ultrasound main irradiation area from theoutside thereof. Further, the wavefront of ultrasound transmitted fromthe transmission transducer elements forms an arc, being a segment of acircle whose center corresponds to the transmission focal point. Here,it should be noted that the ultrasound transmitted from the transmissiontransducer elements does not always converge (i.e., focus) at a singlepoint as described above. That is, transmitted ultrasound may gather atan area (referred to in the following as a transmission focal area)having a width corresponding to half the width of a single transducerelement to several times the width of a single transducer element. Whenultrasound focuses at such an area, the width of the ultrasound mainirradiation area in a direction in which the transducer elements arearrayed (referred to in the following as a transducer element arraydirection) decreases as approaching the transmission focal depth, equalsthe width of the transmission focal area at the transmission focaldepth, and increases once again as departing the transmission focaldepth towards deeper areas. Nevertheless, in either case, the width ofthe ultrasound main irradiation area in the transducer element arraydirection reaches a minimum at the transmission focal depth, andincreases with increasing distance from the transmission focal depth.

Further, with the synthetic aperture method, for each transmissionevent, measurement points covering the entire ultrasound mainirradiation area of the transmission event can be set. As such, it ispreferable that the entirety of the ultrasound main irradiation area beset as a target area, being an area composed of measurement points fromwhich acoustic line signals are to be generated. Meanwhile, a targetarea for one transmission event cannot cover the entirety of an areacorresponding to one frame image. As such, a plurality of transmissionevents, for each of which a different target area is set, need to beconducted to generate one frame image. Taking this into considerationand to increase the efficiency of use of ultrasound, it is preferablethat a target area for a transmission event cover as great an area of anultrasound main irradiation area for the transmission event as possible.Further, in general, to achieve high spatial resolution and high signalS/N ratio, it is preferable that target areas for two consecutivetransmission events overlap one another as much as possible.

In view of the above, typically, a frame acoustic line signal (a groupof acoustic line signals corresponding to one frame image) is generatedby combining a plurality of sub-frame acoustic line signals (each beinga group of acoustic line signals generated in response to onetransmission event), as illustrated in FIG. 28A. Here, each sub-frameacoustic line signal is generated in response to one transmission eventthat is performed by setting the entire hourglass-shaped ultrasound mainirradiation area of the transmission event as the target area for thetransmission event. Further, a plurality of such sub-frame acoustic linesignals are generated while shifting both the ultrasound mainirradiation area and the target area by a shift amount corresponding toa width of a single transducer element between consecutive transmissionevents. When employing this method, the time amount required to generateone frame image equals a product of the time amount required to performa single transmission event and the number of transmission eventsperformed per frame.

As already described above, the synthetic aperture method producesacoustic line signals having high resolution and high signal S/N ratio.However, an increase in frame rate would be desirable in situations suchas where quick acquisition of ultrasound images is desired for reducingstress of the examination subject and the examiner, and where anincrease in time-domain resolution of ultrasound images is desired forexamining movements within the subject, such as blood flow. Achieving anincrease in frame rate requires reducing the time amount required togenerate each frame image. However, this reduction in the time amountrequired to generate a single ultrasound image cannot be achieved byreducing the time amount required for each transmission event, since thetime amount required for a single transmission event is almost uniquelydependent upon ultrasound propagation velocity, and thus, cannot bereduced easily. In view of this, consideration is being made ofachieving an increase in frame rate by reducing the number oftransmission events performed per frame.

A reduction in the number of transmission events performed per frame canbe achieved by increasing the shift amount applied in shifting theultrasound main irradiation area and the target area between consecutivetransmission events. For example, frame rate can be doubled by settingthe shift amount to twice the width of a single transducer element,which equals cutting down the number of sub-frame acoustic line signalsgenerated per frame to ½. Similarly, frame rate can be quadrupled bysetting the shift amount to four times the width of a single transducerelement.

However, when setting the entirety of the hourglass-shaped ultrasoundmain irradiation area as the target area and also setting the shiftamount to at least twice the width of a single transducer element,defective areas as illustrated in FIG. 28B are produced. (Note that inthe present disclosure, an area of an ultrasound image that is notincluded in any target area of any transmission event performed forgenerating the ultrasound image is referred to as a defective area.)FIG. 28B illustrates a case where the shift amount is set to four timesthe width of a single transducer element. In FIG. 28B, the defectiveareas are produced at and around the transmission focal depth, where thewidth of the ultrasound main irradiation areas in the transducer elementarray direction is smaller than the shift amount. Such defective areasare also produced when transmitted ultrasound converges at focus areas,whenever the width of the focus areas in the transducer element arraydirection is smaller than the shift amount. Further, when target areasare set in the inside of ultrasound main irradiation areas, the sameproblem occurs whenever the width of the target areas in the transducerelement array direction at the transmission focal depth is smaller thanthe shift amount. FIG. 26D illustrates one example of an ultrasoundimage in which such defective areas are observed. The arrow in FIG. 26Dindicates focal depth. Here, it should be noted that due to transmittedultrasound converging at the transmission focal depth, strong reflectedultrasound is acquired from areas at and around the transmission focaldepth near which the defective areas are produced. Due to this, thedefective areas tend to stand out in ultrasound images in the form ofvertical stripes. Such stripes lead to a prominent decrease in imagequality at and around the transmission focal depth.

In view of such problems, the present inventor conducted research of atechnology achieving an increase in frame rate while suppressing thedecrease in image quality described above, which would otherwise occurwhen combining the synthetic aperture method with conventionaltransmission beam forming causing wavefront of ultrasound to converge.It is through such research that the present inventor arrived at theultrasound signal processing methods and the ultrasound diagnosticdevices employing such ultrasound signal processing methods described inthe following embodiments.

The following embodiments describe the ultrasound signal processingmethods and the ultrasound diagnostic devices employing such ultrasoundsignal processing methods in detail, with reference to the accompanyingdrawings.

Embodiment 1

<Overall Structure>

The following describes an ultrasound diagnostic device 100 pertainingto embodiment 1, with reference to the accompanying drawings.

FIG. 1 illustrates functional blocks of an ultrasound diagnostic system1000 pertaining to embodiment 1. As illustrated in FIG. 1, theultrasound diagnostic system 1000 includes: a probe 101; the ultrasounddiagnostic device 100; and a display unit 106. The probe 101 includes aplurality of transducer elements 101 a. Each of the transducer elements101 a is capable of transmitting ultrasound towards the subject andreceiving reflected ultrasound (echo signals). The ultrasound diagnosticdevice 100 causes the probe 101 to perform transmission/reception ofultrasound, and generates an ultrasound image based on signals outputfrom the probe 101. The display unit 106 displays the ultrasound imageon any display device provided thereto. The probe 101 and the displayunit 106 are separately connectable to the ultrasound diagnostic device100. FIG. 1 illustrates the ultrasound diagnostic device 100 with theprobe 101 and the display unit 106 connected thereto. Alternatively, theultrasound diagnostic device 100 may include therein the probe 101 andthe display unit 106.

<Structure of Ultrasound Diagnostic Device 100>

The ultrasound diagnostic device 100 includes a multiplexer 102; atransmission beam former 103; and a receive beam former 104. Themultiplexer 102 selects one or more of the transducer elements 101 a forultrasound transmission and one or more of the transducer elements 101 afor ultrasound reception. The multiplexer 102 may select different onesof the transducer elements 101 a for ultrasound transmission andultrasound reception. Further, the multiplexer 102 provides thetransducer elements 101 a for ultrasound transmission with input, andreceives output from the transducer elements 101 a for ultrasoundreception. The transmission beam former 103 controls timings ofapplication of a high voltage for ultrasound transmission to each of thetransducer elements 101 a for ultrasound transmission. The receive beamformer 104 performs some amplification and A/D conversion on electricsignals yielded by the transducer elements 101 a for ultrasoundreception, based on reflected ultrasound received by the probe 101, andperforms receive beam forming to generate acoustic line signals. Inaddition, the ultrasound diagnostic device 100 includes an ultrasoundimage generator 105; a data storage 107; and a control unit 108. Theultrasound image generator 105 generates an ultrasound image (a B-modeimage) based on signals output from the receive beam former 104. Thedata storage 107 stores the acoustic line signal output from the receivebeam former 104 and the ultrasound image output from the ultrasoundimage generator 105. The control unit 108 controls each of the othercomponents of the ultrasound diagnostic device 100.

Among the components of the ultrasound diagnostic device 100, themultiplexer 102, the transmission beam former 103, the receive beamformer 104, and the ultrasound image generator 105 constitute anultrasound signal processing circuit 151, and the ultrasound signalprocessing circuit 151 constitutes an ultrasound signal processingdevice 150.

Each component of the ultrasound diagnostic device 100, for example,each of the multiplexer 102, the transmission beam former 103, thereceive beam former 104, the ultrasound image generator 105, and thecontrol unit 108 may be implemented by using a hardware circuit such asa field-programmable gate array (FPGA), an application-specificintegrated circuit (ASIC), or the like. Alternatively, each of thecomponents may be implemented by using a combination of software and aprogrammable device such as a central processing unit (CPU), aGeneral-purpose computing on graphics processing unit (GPGPU), or anyprocessor. Each of such components may be implemented as one circuitcomponent, or as an aggregate of a plurality of circuit components.Further, a plurality of such components may be implemented by using onecircuit component, or as an aggregate of a plurality of circuitcomponents.

The data storage 107 is a computer-readable recording medium. Forexample, the data storage 107 may be implemented by using a flexibledisk, a hard disk, an MO, a DVD, a DVD-RAM, a BD, or a semiconductormemory. Alternatively, the data storage 107 may be an external storagedevice connected to the ultrasound diagnostic device 100.

Note that the ultrasound diagnostic device 100 pertaining to the presentembodiment need not have the structure illustrated in FIG. 1. Forexample, the ultrasound diagnostic device 100 may not include themultiplexer 102, and the transmission beam former 103 and the receivebeam former 104 may be directly connected with each transducer element101 a of the probe 101. Further, the probe 101 may have built-in thereina part or the entirety of each of the transmission beam former 103, thereceive beam former 104, and the like. Such modifications apply not onlyto the ultrasound diagnostic device 100 pertaining to the presentembodiment, but also similarly apply to the ultrasound diagnosticdevices described later in the other embodiments and modifications inthe present disclosure.

<Structure of Main Part of Ultrasound Diagnostic Device 100>

The ultrasound diagnostic device 100 pertaining to embodiment 1 ischaracterized for including the transmission beam former 103 and thereceive beam former 104. The transmission beam former 103 causes thetransducer elements 101 a of the probe 101 to transmit ultrasound. Thereceive beam former 104 performs computation with respect to electricsignals acquired through the reception of reflected ultrasound by theprobe 101, and generates acoustic line signals used in forming anultrasound image. Accordingly, the present disclosure focuses on thestructure and the functions of each of the transmission beam former 103and the receive beam former 104. Note that components other than thetransmission beam former 103 and the receive beam former 104 may havestructures and functions similar to those in conventional ultrasounddiagnostic devices. In other words, the ultrasound diagnostic device 100may be implemented by replacing beam formers in a conventionalultrasound diagnostic device with the beam formers pertaining to thepresent embodiment.

The following describes the structure of each of the transmission beamformer 103 and the receive beam former 104.

1. Transmission Beam Former 103

The transmission beam former 103 is connected to the probe 101, via themultiplexer 102. However, note that the multiplexer 102 is not amandatory element in the present disclosure. The transmission beamformer 103 controls timings of application of high voltage with respectto each of a plurality of transducer elements 101 a composing atransmission aperture Tx. The transmission aperture Tx is an array oftransducer elements composed of all or some of the transducer elements101 a of the probe 101. Note that in the following, the term“transmission transducer element” is used to refer to transducerelements composing the transmission aperture Tx. The transmission beamformer 103 includes a transmitter 1031.

The transmitter 1031 performs transmission processing. The transmissionprocessing involves supplying a transmission signal having a pulsarwaveform to each of the transmission transducer elements. A transmissiontransducer element receiving a transmission signal transmits anultrasound beam. The transmitter 1031 supplies transmission signals tothe transmission transducer elements based on transmission controlsignals output from the control unit 108. In specific, the transmitter1031 includes, for example, a clock generation circuit, a pulsegeneration circuit, and a delay circuit. The clock generation circuitgenerates a clock signal specifying the transmission timing ofultrasound beams. The pulse generation circuit generates pulse signalsfor driving the transmission transducer elements. The delay circuitperforms focus processing so that ultrasound beams are appropriatelyfocused. In specific, the delay circuit sets a delay time for eachtransmission transducer element, and delays the transmission of theultrasound beam from the transmission transducer element by thecorresponding delay time.

The transmitter 1031 repetitively performs ultrasound transmission whileshifting the transmission aperture Tx in the transducer element arraydirection by a predetermined shift amount Mp each time, so that all ofthe transducer elements 101 a of the probe 101 transmit ultrasound. Theshift amount Mp is at least equal to twice the width of a singletransducer element in the transducer element array direction. Note thatthe present embodiment provides description based on an example wherethe shift amount Mp equals four times the width of a single transducerelement in the transducer element array direction. Thus, in the presentembodiment, transmission apertures Tx corresponding to two consecutivetransmission events differ in position in the transducer element arraydirection by an amount corresponding to four times the width of a singletransducer element. Further, the transmitter 1031 outputs informationindicating the positions of transmission transducer elements composingthe transmission aperture Tx to the data storage 107, via the controlunit 108. For example, supposing that the probe 101 has one hundred andninety two (192) transducer elements 101 a in total, the number oftransmission transducer elements composing the transmission aperture Txmay be twenty (20) to one hundred (100). Further, in the presentdisclosure, the term transmission event is used to refer to ultrasoundtransmission by the transmitter 1031, performed by using onetransmission aperture (i.e., one set of transmission transducer elementsof the predetermined number).

FIG. 2 is a schematic illustrating a propagation path of ultrasoundtransmitted by the transmission beam former 103. FIG. 2 illustrates atransmission aperture Tx for one transmission event (i.e., atransmission transducer element array composed of transmissiontransducer elements 101 a that contribute to ultrasound transmission inthe transmission event). Further, the transmission-array directionlength of the transmission aperture Tx is considered the length of thetransmission aperture Tx.

The transmission beam former 103 controls ultrasound transmission by thetransmission transducer elements such that a transmission transducerelement closer to the center position of the transmission aperture Txtransmits ultrasound later in the transmission event. Due to this, thewavefront of ultrasound transmitted from the transmission transducerelements composing the transmission aperture Tx converges at one pointat a certain focal depth in the subject (i.e., the transmission focalpoint F). Note that the depth of the transmission focal point F (i.e.,transmission focal depth) can be set as desired or required. Afterconverging at the transmission focal point F, the wavefront of thetransmitted ultrasound spreads out as before converging at thetransmission focal point F. Thus, the transmitted ultrasound propagatesthrough an hourglass-shaped area whose base is defined by thetransmission aperture Tx and which is partitioned from other areasinside the subject by two straight lines intersecting at thetransmission focal point F. More specifically, ultrasound transmittedfrom the transmission aperture Tx propagates in the following manner. Asthe transmitted ultrasound advances in a depth direction of the subjectfrom the transmission aperture Tx, the width thereof (length alonghorizontal axis (X axis) in FIG. 2) gradually decreases until reachingthe minimum width at the transmission focal point F. Then, as thetransmitted ultrasound advances further in the depth direction from thetransmission focal point F (i.e., as the ultrasound advances in theupward direction in FIG. 2), the width thereof increases (i.e., theultrasound spreads out). In the following, the hourglass-shaped areadescribed above is referred to as a ultrasound main irradiation area Ax.Note that as already described above, the width of the ultrasound mainirradiation area need not reach a minimum at one point (i.e., thetransmission focal point F), and instead, may reach a minimum at acertain area (i.e., a transmission focal area).

Further, as also described above, the ultrasound main irradiation areaAx is an area in which ultrasound transmitted from the transmissiontransducer elements are in-phase. In the meantime, ultrasoundtransmitted from the transmission transducer elements also propagate tothe outside of the ultrasound main irradiation area Ax. However, phasedifference of the ultrasound transmitted from the different transmissiontransducer elements occurs outside the ultrasound main irradiation areaAx, and thus, the quality of ultrasound transmission waves arriving atpoints outside the ultrasound main irradiation area Ax is lower thanthat of ultrasound transmission waves arriving at points inside theultrasound main irradiation area Ax. More specifically, the greater thedistance from the ultrasound main irradiation area Ax, the lower thequality of ultrasound transmission waves. However, this, in other words,means that ultrasound transmission waves arriving at points close to theultrasound main irradiation area Ax, or more specifically, points withina distance of a few transducer elements from the ultrasound mainirradiation area Ax, has sufficient level to generate beneficialacoustic line signals.

2. Receive Beam Former 104

The receive beam former 104 generates acoustic line signals fromelectric signals acquired by a plurality of transducer elements 101 a.The transducer elements 101 a acquire the electric signals based onreflected ultrasound received by the probe 101. Here, an acoustic linesignal for one measurement point is generated by performingdelay-and-sum processing with respect to receive signals from themeasurement point. Description of the delay-and-sum processing isprovided later in the present disclosure. FIG. 3 is a functional blockdiagram illustrating the structure of the receive beam former 104. Asillustrated in FIG. 3, the receive beam former 104 includes: a receiver1040; a delay-and-sum calculator 1041; and a synthesizer 1140.

The following describes the structure of each functional block of thereceive beam former 104.

(1) Receiver 1040

The receiver 1040 is connected to the probe 101, via the multiplexer102. However, note that the multiplexer 102 is not a mandatory elementin the present disclosure. For each transmission event, the receiver1040 generates receive signals (RF signals). The receiver 1040 generatesthe receive signals by first amplifying electric signals acquiredthrough the probe 101 receiving reflected ultrasound, and thenperforming A/D conversion on the amplified signals. The receiver 1040performs the generation of receive signals for each transmission event,and outputs the receive signals to be stored in the data storage 107.

Here, the receiver 1040 generates one receive signal sequence (RFsignal) for each of some or all of the transducer elements 101 a of theprobe 101. In specific, a receive signal sequence for a given transducerelement is a digital signal yielded by performing A/D conversion on anelectrical signal yielded through conversion of reflected ultrasoundreceived by the transducer element, and is a sequence of signals alongthe ultrasound transmission direction (corresponding to the depthdirection) that are received by the transducer element.

As discussed above, in each transmission event, the transmitter 1031causes the plurality of transmission transducer elements composing thetransmission aperture Tx, among the transducer elements 101 a of theprobe 101, each to transmit an ultrasound beam. Meanwhile, for eachultrasound transmission event, the receiver 1040 generates a receivesignal sequence for each of some or all of the plurality of transducerelements 101 a of the probe 101. The generation of the receive signalsequence for a given one of such transducer elements 101 a is based onreflected ultrasound yielded by the given transducer element 101 a.Here, it is preferable that the number of transducer elements for whichreceive signal sequences are generated be greater than the number oftransmission transducer elements composing the transmission aperture Tx.Further, receive signal sequences may be generated for all of thetransducer elements 101 a of the probe 101.

Further, as already discussed above, the transmitter 1031 repetitivelyperforms transmission events while shifting the transmission aperture Txin the transducer element array direction by the shift amount Mp betweentransmission events, so that all of the transducer elements 101 a of theprobe 101 transmit ultrasound. Meanwhile, for each ultrasoundtransmission event, the receiver 1040 generates a receive signalsequence for each of some or all of the plurality of transducer elements101 a of the probe 101, and stores the receive signal sequences to thedata storage 107.

(2) Delay-and-Sum Calculator 1041

The delay-and-sum calculator 1041 sets a target area Bx for eachtransmission event. A target area Bx is an area in the subject fromwhich one sub-frame acoustic line signal is to be generated. Each targetarea Bx is composed of some of a plurality of measurement points Pij.Further, the delay-and-sum calculator 1041 performs, for eachmeasurement point Pij in the target area Bx, delay-and-sum processingwith respect to receive signal sequences corresponding to themeasurement point Pij, each of which is received by one receivetransducer element Rk. The delay-and-sum calculator 1041 performs thisprocessing for each transmission event having been performed. Thedelay-and-sum calculator 1041, for each transmission event, generates asub-frame acoustic line signal for the transmission event by calculatingan acoustic line signal for each measurement point that is included inthe target area Bx for the transmission event. FIG. 4 is a functionalblock diagram illustrating the structure of the delay-and-sum calculator1041. As illustrated in FIG. 4, the delay-and-sum calculator 1041includes: a target area setter 1042; a receive aperture setter 1043; atransmission time calculator 1044; a receive time calculator 1045; adelay amount calculator 1046; a delay processor 1047; a weightcalculator 1048; and a sum calculator 1049.

The following describes the structure of each functional block of thedelay-and-sum calculator 1041.

i) Target Area Setter 1042

The delay-and-sum calculator 1042 sets the target area Bx, which is anarea in the subject from which one sub-frame acoustic line signal is tobe generated. More specifically, in the present disclosure, the term“target area” is used to indicate a signal area for generating asub-frame acoustic line signal for one transmission event. Further, oneacoustic line signal is generated for each measurement point Pij that isincluded in the target area Bx. In other words, the target area Bx isset for each transmission event in order to specify ones of themeasurement points for which acoustic line signals are to be generatedin response to the transmission event.

Further, in the present disclosure, a sub-frame acoustic line signal isa group of acoustic lines signals that are generated from onetransmission event. As already described above, in response to onetransmission event, a plurality of acoustic line signals are generated,each for a different one of the measurement points Pij included in thetarget area Bx. Further, a sub-frame is a unit corresponding to a groupof signals which are acquired from one transmission event and each ofwhich corresponds to a different one of the measurement points Pij thatare included in the target area Bx for the transmission event. Thus, acombination of multiple sub-frames acquired at different time pointsequals one frame.

For each transmission event, the target area setter 1042 sets a targetarea Bx based on the information indicating the position of thetransmission aperture Tx for the transmission event, which is acquiredfrom the transmission beam former 103.

FIG. 5 is a schematic illustrating one target area Bx. As illustrated inFIG. 5, a target area Bx for a transmission event covers a greater areathan the ultrasound main irradiation area Ax for the transmission event.That is, the target area Bx includes the outside of the ultrasound mainirradiation area Ax. Further, the target area Bx is set so that aminimum width of the target area Bx in the transducer element arraydirection is equal to or greater than the shift amount Mp. For example,in the present embodiment, the target area Bx is yielded by expandingthe hourglass-shaped ultrasound main irradiation area Ax by apredetermined amount, in each of the two directions along the transducerelement array direction. Due to this, the width of the target area Bx inthe transducer element array direction reaches a minimum at thetransmission focal depth. Thus, the target area Bx is set so that theminimum width of the target area Bx in the transducer element arraydirection (referred to in the following as a width Wf) is equal to orgreater than the shift amount Mp. For example, when the shift amount Mpequals four times the width of a single transducer element, it issufficient that the width Wf be set to at least four times the width ofa single transducer element. Further, the width Wf is twice thepredetermined amount described above, which is the amount by which theultrasound main irradiation area Ax is expanded in each of the twodirections along the transducer element array direction to yield thetarget area Bx. Thus, the predetermined amount is at least half theshift amount Mp, and for example, may equal at least three times thewidth of a single transducer element. By setting the target area Bx insuch a manner, the target area Bx is capable of including bothmeasurement points covering substantially the entire ultrasound mainirradiation area Ax and measurement points located in the proximity ofthe ultrasound main irradiation area Ax. This achieves efficient use oftransmitted ultrasound.

However, the target area Bx may have a shape other than theabove-described shape yielded by expanding an hourglass shape in thewidth direction. For example, the target area Bx may have a rectangularshape, with the base set along the subject surface that is in contactwith the transmission transducer element array. Providing the targetarea Bx with such a shape results in the target area Bx includingmeasurement points covering substantially the entire ultrasound mainirradiation area Ax, which also achieves efficient use of transmittedultrasound. However, as already described above, at the outside of theultrasound main irradiation area Ax, the greater the distance from theultrasound main irradiation area Ax, the lower the quality of ultrasoundtransmission waves. Thus, it is preferable that the target area Bxinclude only the ultrasound main irradiation area Ax and the proximityof the ultrasound main irradiation area Ax.

The target area setter 1042 outputs the target area Bx to thetransmission time calculator 1044, the receive time calculator 1045, andthe delay processor 1047.

ii) Receive Aperture Setter 1043

The receive aperture setter 1043 is a circuit that sets, for eachtransmission event, receive apertures Rx based on a control signal fromthe control unit 108 and information from the target area setter 1042indicating the target area Bx for the transmission event. In specific,the receive aperture setter 1043 selects, for each measurement point Pin the target area Bx, some of the transducer elements 101 a of theprobe 101 as receive transducer elements forming a transducer elementarray (referred to in the following as a receive transducer elementarray) whose center position corresponds to a transducer element closestto the measurement point P.

The receive aperture setter 1043 sets, for each measurement point P thatis included in a target area Bx for a transmission event, a receiveaperture Rx (i.e., the receive transducer element array) so that thecenter position of the receive aperture Rx in the transducer elementarray direction corresponds to a transducer element that is spatiallyclosest to the measurement point P. FIG. 6 is a schematic illustratingthe relationship between a transmission aperture Tx and a receiveaperture Rx that the receive aperture setter 1043 sets. As illustratedin FIG. 6, for a given measurement point Pij, the receive aperture Rx isset so that the center position of the receive aperture Rx in thetransducer element array direction corresponds to a transducer elementXk that is spatially closest to the measurement point Pij. Due to this,the position of the receive aperture Rx depends upon the position of themeasurement point P, and does not change depending upon the position ofthe transmission aperture Tx, which shifts each time a transmissionevent is performed. That is, delay-and-sum processing for generating anacoustic line signal for a given measurement point Pij is alwaysperformed based on receive signal sequences acquired by receivetransducer elements Rk composing the same receive aperture Rx. Thismeans that with respect to the measurement point Pij, the same receiveaperture Rx is used in delay-and-sum processing irrespective oftransmission events.

In order to utilize reflected ultrasound from the entirety of theultrasound main irradiation area, the number of the receive transducerelements composing each receive aperture Rx is, beneficially, greaterthan or equal to the number of transmission transducer elementscomposing each transmission aperture Tx. For example, the number ofreceive transducer elements may be 32, 64, 96, 128, 192, and so on.

The setting of the receive apertures Rx is performed for eachtransmission event. Due to this, the setting of the receive aperture Rxis repeated at least for the number of times transmission events areperformed. Further, the setting of receive apertures Rx may be performedeach time a transmission event is performed as described above, oralternatively, receive apertures Rx for multiple transmission eventshaving been performed may be set at once after the completion of thetransmission events.

Further, the receive aperture setter 1043 outputs information indicatingthe positions of the receive transducer elements composing the receiveaperture Rx to the data storage 107, via the control unit 108.

The data storage 107 outputs the information indicating the positions ofthe receive transducer elements composing the receive aperture Rx alongwith receive signal sequences for the receive transducer elements toeach of the transmission time calculator 1044, the receive timecalculator 1045, the delay processor 1047, and the weight calculator1048.

iii) Transmission Time Calculator 1044

The transmission time calculator 1044 is a circuit that, for eachtransmission event, calculates a transmission time for each measurementpoint P that is included in the target area Bx for the transmissionevent. The transmission time for a given measurement point P is the timeamount required for transmitted ultrasound to arrive at the measurementpoint P. The transmission time calculator 1043 acquires informationindicating the positions of the transmission transducer elements for agiven transmission event from the data storage 107, and informationindicating the position of the target area Bx for the transmissionevent, which includes the ultrasound main irradiation area Ax, from thetarget area setter 1042. Based on such information, the transmissiontime calculator 1043, for each measurement point Pij included in thetarget area Bx, calculates the transmission time required fortransmitted ultrasound to arrive at the measurement point Pij.

Each of FIGS. 7A and 7B is a schematic illustrating a propagation pathof ultrasound that is transmitted from the transmission aperture Tx fora transmission event, is then reflected at a measurement point Pij thatis included in the target area Bx for the transmission event, andfinally arrives at a receive transducer element Rk of the receiveaperture Rx. Specifically, FIG. 7A illustrates the propagation path ofultrasound for a measurement point Pij located deeper than thetransmission focal depth, whereas FIG. 7B illustrates the propagationpath of ultrasound for a measurement point Pij located shallower thanthe transmission focal depth. Note that when comparing the position of ameasurement point Pij located deeper than the transmission focal depthand the position of a measurement point Pij located shallower than thetransmission focal depth, the measurement point Pij located deeper thanthe transmission focal depth is located relatively far from the probeand the measurement point Pij located shallower than the transmissionfocal depth is located relatively near to the probe.

Following emission of ultrasound from the transmission aperture Tx, thewavefront of ultrasound converges at the transmission focal point Fafter proceeding along the path 401. Subsequently, the wavefront spreadsout once again and arrives at the measurement point Pij. When there is achange in acoustic impedance at the measurement point Pij, transmittedultrasound generates ultrasound reflection, which is received by thereceive transducer elements Rk of the receive aperture Rx. Thetransmission focal point F is preset in advance upon designing of thetransmission beam former 103. Thus, the length of the path 402 from thetransmission focal point F to the measurement point Pij can becalculated geometrically.

The following describes how the transmission time is calculated infurther detail. Here, note that the calculation of the transmissiontimes for measurement points Pij located outside the ultrasound mainirradiation area Ax is performed in the same manner as the calculationof transmission time for measurement points Pij located inside theultrasound main irradiation area Ax.

First, the calculation of a transmission time for a measurement pointPij located deeper than the transmission focal depth is described, withreference to FIG. 7A. A transmission time for a measurement point Pijlocated deeper than the transmission focal depth is calculated assumingthat ultrasound transmitted from the transmission aperture Tx arrives atthe transmission focal point F by traveling along path 401, and thenarrives at the measurement point Pij by traveling along path 402 fromthe transmission focal point F. As such, the transmission time for sucha measurement point Pij is the total of the time amount required fortransmitted ultrasound to travel through path 401 and the time amountrequired for transmitted ultrasound to travel through path 402.Specifically, the transmission time for such a measurement point Pij canbe calculated, for example, by dividing the total of the lengths ofpaths 401 and 402 by the velocity at which ultrasound propagates withinthe subject.

In the meantime, the following describes the calculation of atransmission time for a measurement point Pij located shallower than thetransmission focal depth, with reference to FIG. 7B. A transmission timefor a measurement point Pij located shallower than the transmissionfocal depth is calculated assuming that the time amount required forultrasound transmitted from the transmission aperture Tx to arrive atthe transmission focal point F by travelling along path 401 equals thetime amount required for ultrasound transmitted from the transmissionaperture Tx to travel along path 404 to arrive at the measurement pointPij and then travel along path 402 to arrive at the transmission focalpoint F from the measurement point Pij. As such, the transmission timefor such a measurement point Pij is calculated by subtracting the timeamount required for transmitted ultrasound to travel through the path402 from the time amount required for transmitted ultrasound to travelthrough the path 401. Specifically, a transmission time for such ameasurement point Pij can be calculated, for example, by dividing thevalue acquired by subtracting the length of path 401 from the length ofpath 401, by the velocity at which ultrasound propagates within thesubject.

Note that in the present embodiment, a transmission time for ameasurement point Pij located at the transmission focal depth iscalculated in the same way as the transmission time for a measurementpoint Pij located deeper than the transmission focal depth. That is, atransmission time for a measurement point Pij located at thetransmission focal depth is calculated by using the total of the timeamount required for transmitted ultrasound to travel through path 401and the time amount required for transmitted ultrasound to travelthrough path 402. Alternatively, a transmission time for a measurementpoint Pij located at the transmission focal depth may be calculated inthe same way as the transmission time for a measurement point Pijlocated shallower than the transmission focal depth, or that is by usinga value obtained by subtracting the time amount required for transmittedultrasound to travel through the path 402 from the time amount requiredfor transmitted ultrasound to travel through the path 401. However, itshould be noted that in either case, it is preferable that for a singletransmission event, the calculation of transmission times for multiplemeasurement points Pij located at the transmission focal depth beperformed according to the same one of the above-described methods. Thisis since, when in response to a single transmission event, thecalculation of transmission times for some measurement points Pijlocated at the transmission focal depth is performed by using thecalculation method for measurement points Pij located deeper than thetransmission focal depth and the calculation of transmission times forthe rest of the measurement point Pij located at the transmission focaldepth is performed by using the calculation method for measurementpoints Pij located shallower than the transmission focal depth, aconsiderable gap may occur between the transmission times of twomeasurement points Pij adjacent in the transducer element arraydirection. This may result in insufficient image quality improvement.

For each transmission event, the transmission time calculator 1044calculates the transmission time for each measurement point Pij in thetarget area Bx for the transmission event. That is, the transmissiontime calculator 1044 calculates, for each measurement point Pij, thetime amount required for transmitted ultrasound to arrive at themeasurement point Pij. Further, the transmission time calculator 1044outputs the transmission time so calculated to the delay amountcalculator 1046.

iv) Receive Time Calculator 1045

The receive time calculator 1045 is a circuit that calculates, for eachmeasurement point P, a receive time required for ultrasound reflectionfrom the measurement point P to arrive at each receive transducerelement Rk of the receive aperture Rx. For a given transmission event,the receive time calculator 1045 acquires information indicating thepositions of the receive transducer elements Rk for the giventransmission event from the data storage 107, and acquires theinformation indicating the position of the target area Bx for the giventransmission event from the target area setter 1042. Based on suchinformation, the receive time calculator 1045, for each measurementpoint Pij in the target area Bx, calculates the receive time requiredfor transmitted ultrasound to arrive at each receive transducer elementRk after being reflected at the measurement point Pij.

As already discussed above, transmitted ultrasound arriving at ameasurement point Pij generates ultrasound reflection when there is achange in acoustic impedance at the measurement point Pij. The reflectedultrasound is then received by receive transducer elements Rk of thereceive aperture Rx. As discussed above, the receive time calculator1045 acquires information indicating the positions of the receivetransducer elements Rk of the receive aperture Rx from the data storage107. Accordingly, the receive time calculator 1045 is able togeometrically calculate the length of paths 403 leading from themeasurement point Pij to the respective receive transducer elements Rk.

For each transmission event, the receive time calculator 1045 calculatesthe receive time for each measurement point Pij that is included in thetarget area Bx for the transmission event. That is, the receive timecalculator 1045 calculates, for each measurement point Pij, the timerequired for transmitted ultrasound to arrive at each receive transducerelement Rk after being reflected at the measurement point Pij. Further,the receive time calculator 1045 outputs the receive time so calculatedto the delay amount calculator 1046.

v) Delay Amount Calculator 1046

The delay amount calculator 1046 is a circuit that calculates, for eachreceive transducer element Rk, a total propagation time based on thetransmission time and the receive time for the receive transducerelement Rk. Further, the delay amount calculator 1046 calculates, foreach receive transducer element Rk, a delay amount to be applied to areceive signal sequence for the receive transducer element Rk. Inspecific, the delay amount calculator 1046 acquires, from thetransmission time calculator 1044, the transmission time required forultrasound waves to arrive at a measurement point Pij. Further, for eachreceive transducer element Rk, the delay amount calculator 1046acquires, from the receive time calculator 1045, the receive timerequired for ultrasound to be reflected at the measurement point Pij andarrive at the receive transducer element Rk. Then, the delay amountcalculator 1046, for each receive transducer Rk, calculates a totalpropagation time required for transmitted ultrasound to arrive at thereceive transducer element Rk. Further, based on the difference betweentotal propagation times for the receive transducer elements Rk, thedelay amount calculator 1046 calculates a delay amount for each receivetransducer element Rk. For each measurement point P that is included inthe target area Bx, the delay amount calculator 1046 calculates, foreach receive transducer element Rk, the delay amount to be applied to areceive signal sequence for the receive transducer element Rk, andoutputs the delay amounts to the delay processor 1047.

vi) Delay Processor 1047

The delay processor 1047 is a circuit that specifies, for each receivetransducer element Rk, a receive signal based on reflected ultrasoundfrom a measurement point Pij. In specific, for each receive transducerelement Rk, the delay processor 1047 specifies a receive signalcorresponding to the delay amount for the receive transducer element Rkfrom the receive signal sequence for the receive transducer element Rk.

More specifically, for each transmission event, the delay processor 1047acquires, for each receive transducer element Rk, information indicatingthe position of the receive transducer element Rk from the receiveaperture setter 1043, the receive signal sequence for the receivetransducer element Rk from the data storage 107, and the delay amount tobe applied to the receive signal sequence of the receive transducerelement Rk from the delay amount calculator 1046. In addition, for eachtransmission event, the delay processor 1047 acquires the informationindicating the position of the target area Bx from the target areasetter 1042. Further, for each receive transducer element Rk, the delayprocessor 1047 specifies a receive signal based on reflected ultrasoundfrom a measurement point Pij. In specific, the delay processor 1047specifies, from the receive signal sequence for the receive transducerelement Rk, a receive signal corresponding to a time point aftersubtraction of the delay amount for the receive transducer element Rk.The delay processor 1047 outputs the receive signal so specified to thesum calculator 1049.

vii) Weight Calculator 1048

The weight calculator 1048 is a circuit that calculates a weightsequence (reception apodization weight) for the receive transducerelements Rk, so that the maximum weight is set with respect to thereceive transducer element located at the center of the receive apertureRx in the transducer element array direction.

As illustrated in FIG. 6, the weight sequence is a numerical sequence ofweight coefficients that are to be applied to receive signals for thereceive transducer elements composing the receive aperture Rx. Theweight sequence indicates weights that are distributed symmetricallywith respect to the measurement point Pij. As the shape of distributionof the weights indicated by the weight sequence, any shape isapplicable, including but not limited to a hamming window, a hanningwindow, and a rectangular window. The weight sequence is set so that themaximum weight is set with respect to the receive transducer elementlocated at the center position of the receive aperture Rx in thetransducer element array direction, and the central axis of the weightdistribution corresponds to the center axis Rxo of the receive apertureRx. The weight calculator 1048 uses as input information indicating thepositions of the receive transducer elements Rk, which is output fromthe receive aperture setter 1043, and outputs the weight sequence forthe receive transducer elements Rk to the sum calculator 1049.

viii) Sum Calculator 1049

The sum calculator 1049 is a circuit that generates a delayed-and-summedacoustic line signal for each measurement point P, by using as input thespecified receive signals for the receive transducer elements Rk, whichare output from the delay processor 1047, and summing together thespecified receive signals. Alternatively, the sum calculator 1049 maygenerate an acoustic line signal for each measurement point P by usingas input the weight numerical sequence for the receive transducerelements Rk, which is output from the weighting calculator 1048,multiplying the specified receive signal for each receive transducerelement Rk with a corresponding weight, and summing the weighted receivesignals. The sum calculator 1049 sums the receive signals for thereceive transducer elements Rk, after the receive signals have been putin the same phase by the delay processor 1047. Due to this, the sumcalculator 1049 is capable of increasing the S/N ratio of the receivesignals received by the receive transducer elements Rk based onreflected ultrasound from the measurement point Pij, and receive signalsfor the measurement point Pij can be extracted.

As a result of one transmission event and processing accompanying thetransmission event, an acoustic line signal is generated for eachmeasurement point P in the target area Bx for the transmission event,which includes the ultrasound main irradiation area Ax. Further, byrepetitively performing transmission events while shifting thetransmission aperture Tx in the transducer element array direction bythe shift amount Mp each time, all of the transducer elements 101 a inthe probe 101 perform ultrasound transmission. Due to this, a frameacoustic line signal, which is a combination of acoustic line signalscorresponding to one frame, is generated.

In the present embodiment, acoustic line signals for respectivemeasurement points, which compose the frame acoustic line signal andeach of which is generated by combining a plurality of acoustic linessignals corresponding to the measurement point that are included indifferent sub-frame acoustic line signals, are each referred to as acombined acoustic line signal for the measurement point.

The sum calculator 1049, for each transmission event, generates asub-frame acoustic line signal being a combination of acoustic linesignals for every measurement point Pij within the target area Bx forthe transmission event. Further, the sum calculator 1049 outputs thesub-frame acoustic line signals so generated to be stored in the datastorage 107.

(5) Synthesizer 1140

The synthesizer 1140 is a circuit that generates a frame acoustic linesignal by combining a plurality of sub-frame acoustic line signals eachgenerated for one transmission event. FIG. 8 is a functional blockdiagram illustrating the structure of the synthesizer 1140. Asillustrated in FIG. 8, the synthesizer 1140 includes an adder 11401 andan amplifier 11402.

The following describes the structure of each functional block of thesynthesizer 1140.

i) Adder 11401

The adder 11401, after the generation of a series of sub-frame acousticline signals necessary for generating one frame acoustic line signal iscompleted, reads out the sub-frame acoustic line signals from the datastorage 107. Further, the adder 11401 generates a frame acoustic linesignal by combining the plurality of sub-frame acoustic line signals.The combining of the sub-frame acoustic line signals is performedaccording to the positions of the measurement points Pij, such that inthe process, a combined acoustic line signal is generated for eachmeasurement point Pij. In specific, the adder 11401 generates a combinedacoustic line signal for a given measurement point Pij by combining aplurality of acoustic line signals corresponding to the measurementpoint Pij that are included in different sub-frame acoustic linesignals. Due to this, acoustic line signals for the same measurementpoint that are included in different sub-frame acoustic line signals arecombined, to generate a combined acoustic line signal for themeasurement point.

FIG. 9 is a schematic illustrating processing by the adder 11401 forgenerating a combined acoustic line signal. As already discussed above,ultrasound transmission is performed by repetitively performingtransmission events while shifting the transmission transducer elementarray (i.e., the transmission aperture Tx) in the transducer elementarray direction by the shift amount Mp each time. Due to this, targetareas Bx for two consecutive transmission events, each of whichincluding the ultrasound main irradiation area Ax based on one of theconsecutive transmission events, differ in position from one another inthe transducer element array direction by the shift amount Mp. Thus, aframe acoustic line signal covering all target areas Bx can be generatedby combining sub-frame acoustic line signals based on the positions ofthe measurement points Pij from which the acoustic lines signalsincluded in the sub-frame acoustic line signals are acquired.

Further, for a measurement point included in multiple target areas Bx,values of a plurality of acoustic line signals included in differentsub-frame acoustic line signals are summed. Thus, the combined acousticline signal for such a measurement point may indicate a great value,depending upon the number of target areas Bx in which the measurementpoint is included. In the following, the number of different targetareas Bx in which a given measurement point is included is referred toas an overlap count of the measurement point, and the maximum value ofthe overlap count in the transducer element array direction is referredto as a maximum overlap count. As already described above, each targetarea Bx is set so that at the transmission focal depth, the width Wf ofthe target area Bx in the transducer element array direction is equal toor greater than the shift amount Mp. Due to this, at the transmissionfocal depth, the overlap count is at least one (not zero), or in otherwords, each measurement point Pij at the transmission focal depth isincluded in at least one target area Bx.

Further, in the present embodiment, the target area Bx has anhourglass-shape. Due to this, the overlap count and the maximum overlapcount differ in the depth direction of the subject, as illustrated inFIG. 10A. Accordingly, combined acoustic line signals for measurementpoints at different depths also have different values.

Note that in combining sub-frame acoustic line signals based on thepositions of the measurement points Pij from which the acoustic linessignals included in the sub-frame acoustic line signals are acquired togenerate combined acoustic line signals for the respective measurementpoints, the adder 11401 may add weights in accordance with the positionsof the measurement points Pij.

The adder 11401 outputs the frame acoustic line signal so generated tothe amplifier 10492.

ii) Amplifier 11402

As already described above, the value of a combined acoustic line signalfor a given measurement point is dependent upon the maximum overlapcount at the measurement point. In addition, the overlap count alsochanges in the depth direction. In order to moderate such variationbetween values of different combined acoustic line signals, theamplifier 11402, in combining the combined acoustic line signals togenerate the frame acoustic line signal, performs amplification ofmultiplying the combined acoustic line signals by amplification factors.Here, the amplifier 11402 determines an amplification factor for a givencombined acoustic line signal according to the number of acoustic linesignals combined to yield the combined acoustic line signal.

FIG. 10B is a schematic providing an overview of the amplificationperformed by the amplifier 11402. The maximum overlap count varies inthe depth direction, as illustrated in FIG. 10A. Thus, to compensatewith this variation in maximum overlap count, the amplifier 11402multiplies the combined acoustic line signals by respectiveamplification factors that are based on the maximum overlap counts andvary in the depth direction, as illustrated in FIG. 10B. Here, theamplification factors used by the amplifier 11402 are such that, thegreater the width of the target area Bx in the transducer element arraydirection, the greater the difference between the amplification factorsin the depth direction. This moderates a difference between values ofcombined acoustic line signals deriving from the difference in overlapcounts in the depth direction, and thus, the values of the combinedacoustic line signals after the amplification are averaged out in thedepth direction. That is, the amplification performed by the amplifier11402 is gain equalization in the depth direction.

Further, the amplifier 11402 may also multiply the combined acousticline signals by amplification factors varying in the transducer elementarray direction that are calculated based on overlap counts, whenoverlap counts vary in the transducer element array direction. Thismoderates a difference between values of combined acoustic line signalsderiving from the difference in overlap counts in the transducer elementarray direction, and thus, the values of the combined acoustic linesignals after the amplification are averaged out in the transducerelement array direction.

Here, note that the amplifier 11402 may generate the frame acoustic linesignal by combining amplified combined acoustic line signals forrespective measurement points.

<Operations>

The following describes the operations of the ultrasound diagnosticdevice 100 having the structure described up to this point.

FIG. 11 is a flowchart illustrating beam forming by the receive beamformer 104.

First, in Step S101, the transmitter 1031 performs transmissionprocessing (a transmission event) of supplying a transmission signalcausing transmission of an ultrasound beam to each transmissiontransducer element of the transmission aperture Tx.

In Step S102, the receiver 1040 generates receive signal sequences basedon electric signals yielded through the reception of reflectedultrasound by the probe 101, and outputs the receive signal sequences tobe stored in the data storage 107. Then, a determination is made ofwhether or not all transducer elements 101 a of the probe 101 haveperformed ultrasound transmission (S103). When one or more of thetransducer elements 101 a have not yet performed ultrasoundtransmission, processing returns to Step S101, which results in anothertransmission event being executed by shifting the transmission apertureTx in the transducer element array direction by a shift amount Mp.Meanwhile, when all of the transducer elements 101 a have performedultrasound transmission, processing proceeds to Step S210.

In Step S210, the target area setter 1042 sets a target area Bx for aprocessing-target transmission event based on information indicating theposition of the transmission aperture Tx for the processing-targettransmission event and the shift amount Mp. In the initial loop ofprocessing, the target area setter 1042 sets a target area Bx includingthe ultrasound main irradiation area Ax for the initial transmissionevent, which can be calculated from the transmission aperture Tx for theinitial transmission event.

Subsequently, processing proceeds to measurement-point dependent beamforming (Step S220 (including Steps S221 through S228)). In Step S220,first, coordinate values i and j indicating a position of a measurementpoint Pij that is included in the target area Bx for theprocessing-target transmission event are initialized (set to therespective minimum possible values in the target area Bx) (Steps S221and S222). Then, the receive aperture setter 1043 sets a receiveaperture Rx for the current measurement point so that the center of thereceive aperture Rx corresponds to a transducer element Xk that isspatially closest to the current measurement point Pij (Step S223).

Subsequently, an acoustic line signal is generated for the currentmeasurement point Pij (Step S224).

The following describes the operations in Step S224 for generating anacoustic line signal for the current measurement point Pij. FIG. 12 is aflowchart illustrating the operations of the receive beam former 104 forgenerating the acoustic line signal for the current measurement pointPij. FIG. 13 is a schematic for explaining the operations of the receivebeam former 104 for generating the acoustic line signal for the currentmeasurement point Pij.

First, in Step S2241, the transmission time calculator 1044 calculates,for the current measurement point Pij, a transmission time required fortransmitted ultrasound to arrive at the current measurement point Pij.As already described above, the current measurement point Pij is ameasurement point included in the target area Bx for theprocessing-target transmission event. Here, (i) when the currentmeasurement point Pij is located at the transmission focal depth ordeeper than the transmission focal depth, the transmission time for thecurrent measurement point Pij is calculated by dividing, by ultrasoundvelocity cs, the geometrically-calculatable length of a path(combination of paths 401 and 402) starting at a transmission transducerelement in the transmission aperture Tx and reaching the currentmeasurement point Pij via the transmission focal point F. Meanwhile,(ii) when the current measurement point Pij is located shallower thanthe transmission focal depth, the transmission time for the currentmeasurement point is calculated by dividing, by the ultrasound velocitycs, a value (401-402) obtained by subtracting thegeometrically-calculatable length of the path from the transmissionfocal point F to the current measurement point Pij from thegeometrically-calculatable length of the path from a transmissiontransducer element in the transmission aperture Tx to the transmissionfocal point F.

Subsequently, value k, which indicates the position of a target receivetransducer element Rk of the receive aperture Rx, is initialized (set tothe minimum possible value in the receive aperture Rx) (Step S2242).Then, the receive time for the target receive transducer element Rk iscalculated (Step S2243). The receive time is the time required fortransmitted ultrasound to arrive at the target receive transducerelement Rk after being reflected at the current measurement point Pij.The receive time for the target receive transducer element Rk can becalculated by dividing, by the ultrasound velocity cs, thegeometrically-calculatable length of the path 403 from the currentmeasurement point Pij to the target receive transducer element Rk.Further, from a sum of the transmission time and the receive time forthe target receive transducer element Rk, the total propagation timerequired for ultrasound transmitted from the transmission aperture Tx toarrive at the target receive transducer element Rk after being reflectedat the current measurement point Pij is calculated (Step S2244).Further, based on the difference in total propagation time betweendifferent receive transducer elements Rk composing the receive apertureRx, the delay amount for the target receive transducer element Rk iscalculated (Step S2245).

Subsequently, a determination is performed of whether or not a delayamount has been calculated for every receive transducer element Rkcomposing the receive aperture Rx (Step S2246). When a delay amount hasnot yet been calculated for one or more of the receive transducerelements Rk, the value k is incremented (Step S2247), and a delay amountfor another receive transducer element Rk is calculated (Step S2243).Meanwhile, when a delay amount has been calculated for every receivetransducer element Rk composing the receive aperture Rx, processingproceeds to Step S2248. Note that at this point, a delay amount for thecurrent measurement point Pij has already been calculated for eachreceive transducer element Rk of the receive aperture Rx. The delayamount for a given receive transducer element Rk indicates delay withwhich reflected ultrasound from the current measurement point Pijarrives at the receive transducer element Rk.

In Step S2248, the delay processor 1047, for each receive transducerelement Rk, specifies a receive signal based on reflected ultrasoundfrom the current measurement point Pij. Here, the delay processor 1047specifies, from a receive signal sequence corresponding to each receivetransducer element Rk, a receive signal corresponding to a time pointafter subtraction of the delay amount for the receive transducer elementRk.

Subsequently, the weight calculator 1048 calculates a weight sequencefor the receive transducer elements Rk of the current receive apertureRx, so that the maximum weight is set with respect to the receivetransducer element located at the center position of the receiveaperture Rx in the transducer element array direction (S2249). Then, thesum calculator 1049 generates an acoustic line signal for the currentmeasurement point Pij by multiplying the specified receive signal foreach receive transducer element Rk by a weight corresponding to thereceive transducer element Rk, and summing the weighted receive signalsfor the different receive transducer elements Rk (Step S2250). Followingthis, the sum calculator 1049 outputs the acoustic line signal for thecurrent measurement point Pij to the data storage 107 to be stored inthe data storage 107 (Step S2251).

Referring to FIG. 11 once again, subsequently, an acoustic line signalis generated for each measurement point Pij (each illustrated in FIG. 13as a black dot) that is included in the target area Bx for theprocessing-target transmission event, by repeating Steps S223, S224while incrementing the coordinate values i and j (Steps S225, S227).Subsequently, a determination is performed of whether or not an acousticline signal has been generated for every measurement point Pij withinthe target area Bx. When an acoustic line signal has not yet beengenerated for every measurement point Pij within the target area Bx, thecoordinate values i and j are incremented, yielding an acoustic linesignal for another measurement point Pij (Step S224). Meanwhile, when anacoustic line signal has already been generated for every measurementpoint Pij within the target area Bx, processing proceeds to Step S230.At this point, an acoustic line signal has already been generated foreach measurement point P that is included in the target area Bxcorresponding to the processing-target transmission event, and theacoustic line signals have been output to and stored to the data storage107. In other words, a sub-frame acoustic line signal for theprocessing-target transmission event has been generated, and output toand stored to the data storage 107.

Subsequently, a determination is performed of whether or not a sub-frameacoustic line signal has been generated for each transmission eventhaving been performed (Step S230). When sub-frame acoustic line signalshave not yet been generated for one or more transmission events,processing proceeds to Step S210, where the coordinate values i and jare initialized (set to the respective minimum possible values in thetarget area Bx for the subsequent transmission event, which can becalculated from the transmission aperture Tx for the subsequenttransmission event) (Steps S221 and S222), and then setting of a receiveaperture Rx is performed (Step S223). Meanwhile, when sub-frame acousticline signals have been generated for every transmission event havingbeen performed, processing proceeds to Step S301.

In Step S301, the adder 11401 reads out the sub-frame acoustic linesignals stored in the data storage 107, and combines the sub-frameacoustic line signals based on positions of the measurement points Pij.Thus, a combined acoustic line signal is generated for each measurementpoint Pij, and accordingly, a frame acoustic line signal is generated.Subsequently, the amplifier 11402 multiples each combined acoustic linesignal by a corresponding amplification factor that is determined basedon the number of acoustic line signals, included in the sub-frameacoustic line signals, that have been combined to yield the combinedacoustic line signal (Step S302). Further, the amplifier 11402 outputsthe amplified frame acoustic line signal to the ultrasound imagegenerator 105 and the data storage 107 (Step S303), and processing isterminated.

<Conclusion>

As described above, the ultrasound diagnostic device 100 pertaining tothe present embodiment, according to the synthetic aperture method,synthesizes acoustic line signals for the same measurement point thatare generated in response to different transmission events. Thisachieves the effect of performing, for multiple transmission events,virtual transmission focusing even for measurement points that arelocated in depths other than that of the transmission focal point F.This improves spatial resolution and S/N ratio.

In addition, in the ultrasound diagnostic apparatus 100, a target area,which is an area from which a sub-frame acoustic line signal isgenerated, is set to have a width equal to or greater than the width ofthe shift amount in the transducer element array direction. Due to this,regardless of the width of the shift amount, a defective area (i.e., anarea where overlap count is zero) is not formed between any two targetareas corresponding to two consecutive transmission events. Due to this,the ultrasound diagnostic apparatus 100 prevents image quality reductionbrought about by the occurrence of such defective areas and is capableof achieving high frame rate, even when the shift amount is providedwith a great value.

Further, in the ultrasound diagnostic device 100, the receive aperturesetter 1043 selects, as transducer elements composing the receiveaperture Rx for each measurement point P, transducer elements forming anarray whose center position in the transducer element array directionmatches a transducer element that is spatially closest to themeasurement point P. Accordingly, the ultrasound diagnostic device 100performs receive beam forming by using a receive aperture that is notdependent upon ultrasound transmission events but is dependent upon theposition of the measurement point P, and that is symmetric with respectto the measurement point P. Due to this, the receive aperture Rx for agiven measurement point P does not change (i.e., the same receiveaperture Rx is used for the same measurement point P) between differenttransmission events, between which the transmission focal point F isshifted in the transducer element array direction. Thus, delay-and-sumprocessing for the same measurement point P is always performed by usingthe same receive aperture Rx. In addition, in the ultrasound diagnosticdevice 100, a weight sequence is set so that the closer a receivetransducer element is to the measurement point P, the greater the weightapplied to the receive transducer element. Due to this, even taking intoaccount the fact that ultrasound decay increases as propagation distanceincreases, ultrasound reflected from the measurement point P can be usedwith high efficiency. Accordingly, the ultrasound diagnostic device 100achieves both high local spatial resolution and high S/N ratio.

<<Modification 1>>

The receive aperture setter 1043 in the ultrasound diagnostic device 100pertaining to embodiment 1 sets, for each measurement point P, thereceive aperture Rx so that the center position of the receive apertureRx in the transducer element array direction corresponds to a transducerelement that is spatially closest to the measurement point P. However,the configuration of the receive aperture Rx may be changed asnecessary, as long as acoustic line signals for all measurement pointsPij that are included in each target area Bx can be generated bycalculating total propagation times and performing delaying based ontotal propagation paths. As already discussed above, a total propagationtime for a given receive transducer element Rk is the time required forultrasound transmitted from the transmission aperture Tx to reach thereceive transducer element Rk after passing through the transmissionfocal point F and being reflected at the measurement point P.

Modification 1 provides an ultrasound diagnostic device differing fromthe ultrasound diagnostic device 100 pertaining to embodiment 1 forincluding a receive aperture setter (a Tx receive aperture setter) thatsets, for each transmission event, the receive aperture Rx so that thecenter position of the receive aperture Rx corresponds to the centerposition of the transmission aperture Tx for the transmission event.That is, the receive aperture Rx in modification 1 can be referred to asa transmission-dependent receive aperture. Other than the Tx receiveaperture setter, the components of the ultrasound diagnostic devicepertaining to modification 1 have the same structures and configurationsas the corresponding components in the ultrasound diagnostic device 100described in embodiment 1. Thus, description of such similar componentsis not provided in the following.

FIG. 14 is a schematic illustrating the relationship between atransmission aperture Tx and a receive aperture Rx set by the Tx receiveaperture setter. In modification 1, the Tx receive aperture setter sets,for each transmission event, a receive aperture Rx so that the centerposition of the receive aperture Rx in the transmission element arraydirection corresponds to the center position of the transmissionaperture Tx for the transmission event. Thus, the position of an axisRxo passing through the center position of the receive aperture Rxcorresponds to the position of an axis Txo passing through the centerposition of the transmission aperture Tx. Further, the receive apertureRx is symmetric about the transmission focal point F (i.e., has the samenumber of apertures at both sides of the center position thereof in thetransmission element array direction). As such, as the transmissionaperture Tx shifts in the transducer element array direction from onetransmission event to another, the receive aperture Rx also shifts inthe transducer element array direction, following the transmissionaperture Tx.

In addition, a weight sequence (so-called reception apodization weight)for the receive transducer elements Rk is calculated, so that themaximum weight is set with respect to the receive transducer element Rklocated along the center axis Rxo of the receive aperture Rx and thecenter axis Txo of the transmission aperture Tx. The weight sequenceindicates weights distributed symmetrically with respect to the centeraxis Txo of the transmission aperture Tx. As the shape of distributionof the weights indicated by the weight sequence, any shape isapplicable, including but not limited to a hamming window, a hanningwindow, and a rectangular window.

<Operations>

FIG. 15 is a flowchart illustrating beam forming by a receive beamformer of the ultrasound diagnostic device pertaining to modification 1.The flowchart in FIG. 15 differs from the flowchart in FIG. 11 fortransmission-dependent dependent beam forming (Step S420 (includingSteps S421 through S428)) being performed in place of measurementpoint-dependent beam forming (Step S220 (including Steps S221 throughS228)). Meanwhile, the processing in steps other than

Step S420 in the flowchart in FIG. 15 is similar to the processing inthe corresponding steps in the flowchart in FIG. 11. Thus, descriptionof such similar processing is not provided in the following.

In Step S420, first, the Tx receive aperture setter sets a receiveaperture Rx for a transmission event by selecting receive transducerelements Rk composing a receive transducer element array whose centerposition matches the center position of the transducer element arraycomposing the transmission aperture Tx for the correspondingtransmission event, in Step S421.

Subsequently, coordinate values i and j indicating a position of ameasurement point Pij that is included in the target area Bx for theprocessing-target transmission event are initialized (set to therespective minimum possible values in the target area Bx set in StepS210) (Steps S422 and S423). Subsequently, an acoustic line signal isgenerated for the current measurement point Pij (Step S424). FIG. 16 isa schematic for explaining the operations of the receive beam formerpertaining to modification 1 for generating the acoustic line signal forthe current measurement point Pij. FIG. 16 differs from FIG. 13 referredto in embodiment 1 in terms of the positional relationship between thetransmission aperture Tx and the receive aperture Rx. The processing inStep S424 is similar to that in Step S224 of FIG. 11 (i.e., Steps S2241through S2251 in FIG. 12).

An acoustic line signal is generated for each measurement point Pij(each illustrated in FIG. 16 as a black dot) that is included in thetarget area Bx by repeating Step S424 while incrementing the coordinatevalues i and j. Subsequently, a determination is performed of whether ornot an acoustic line signal has been generated for one or more of themeasurement points Pij included in the target area Bx (Steps S425,S427). When an acoustic line signal has not yet been generated for everymeasurement point Pij within the target area Bx, the coordinate values iand j are incremented (Steps S426 and S428), yielding an acoustic linesignal for another measurement point Pij (Step S424). Meanwhile, when anacoustic line signal has already been generated for every measurementpoint Pij within the target area Bx, processing proceeds to Step S230.At this point, an acoustic line signal has already been generated foreach measurement point Pij that is included in the target area Bx forthe processing-target transmission event, and the acoustic line signalshave been output to and stored to the data storage 107.

<Effects>

The ultrasound diagnostic device pertaining to modification 1, which hasbeen described up to this point, achieves the effects described inembodiment 1, excluding the effect related to setting a measurementpoint-dependent receive aperture. In place of the effect related tosetting a measurement point-dependent receive aperture, the ultrasounddiagnostic device pertaining to modification 1 achieves the followingeffect. In modification 1, for each transmission event, the receiveaperture Rx is set by selecting receive transducer elements forming atransducer element array whose center position corresponds to the centerposition of the transducer element array composing the transmissionaperture Tx for the transmission event. Due to this, the position of thecentral axis Rxo of the receive aperture Rx for a given transmissionevent corresponds to the position of the central axis Txo of thetransmission aperture Tx for the same transmission event. Further, whentransmission events are repetitively performed, the transmissionaperture Tx shifts in the transducer element array direction each time,and the receive aperture Rx also shifts in the transducer element arraydirection in synchronization with the transmission aperture Tx. Thus, adifferent receive aperture is used to perform delay-and-sum for eachtransmission event. Accordingly, receive processing with respect tomultiple transmission events can be performed by using a group ofreceive apertures covering a vast measurement area and each differing interms of time. Thus, uniform spatial resolution is achieved over a vastmeasurement area.

Embodiment 2

The ultrasound diagnostic apparatus 100 includes the delay-and-sumprocessor 1041, which generates sub-frame acoustic line signals, and thesynthesizer 1140, which combines the sub-frame acoustic signals togenerate a frame acoustic line signal. Here, it should be noted that inembodiment 1, no distinction is made between measurement points insidethe ultrasound main irradiation area Ax and measurement points outsidethe ultrasound main irradiation area Ax in the generation of sub-frameacoustic line signals. However, acoustic line signals generated frommeasurement points outside the ultrasound main irradiation area Ax, whencompared with acoustic line signals generated from measurement pointsinside the ultrasound main irradiation area Ax, have lower spatialresolution and lower signal S/N ratio. This is since, as alreadydescribed above, amplitude of transmitted ultrasound decreases and phasedifference of transmitted ultrasound increases outside the ultrasoundmain irradiation area Ax. Accordingly, if one measurement point Pij isincluded in target areas Bx for two transmission events (a firsttransmission event and a second transmission event), is inside theultrasound main irradiation area Ax of the target area Bx for the firsttransmission event, and is outside the ultrasound main irradiation areaAx of the target area Bx for the second transmission event, themeasurement point Pij yields an acoustic line signal having high spatialresolution and high S/N ratio for the first transmission event and anacoustic line signal having low spatial resolution and low S/N ratio forthe second transmission event. Nevertheless, in the generation of theframe acoustic line signal, a sub-frame acoustic line signalcorresponding to the first transmission event and a sub-frame acousticline signal corresponding to the second transmission event are combined,while the spatial resolution and S/N ratio for the measurement point Pijis high in the sub-frame acoustic line signal corresponding to the firsttransmission event and is low in the sub-frame acoustic line signalcorresponding to the second transmission event. However, it should benoted that in this case, ultrasound image quality for the measurementpoint Pij is higher when using only the sub-frame acoustic line signalfor the first transmission event.

Embodiment 2 describes an ultrasound diagnostic device that differs fromthe ultrasound diagnostic device 100 pertaining to embodiment 1 for: (i)separately generating a sub-frame acoustic line signal corresponding tothe outside of the ultrasound main irradiation area Ax and a sub-frameacoustic line signal corresponding to the inside of the ultrasound mainirradiation area Ax; (ii) combining multiple sub-frame acoustic linesignals corresponding to the outside of the ultrasound main irradiationarea Ax with one another and combining multiple sub-frame acoustic linesignals corresponding to the inside of the ultrasound main irradiationarea Ax with one another; and (iii) generating a frame acoustic linesignal by combining the results of such separate combining.

<Structure>

The following describes the ultrasound diagnostic device pertaining toembodiment 2, with reference to the accompanying drawings. FIG. 17 is afunctional block diagram illustrating the structure of a receive beamformer 104A of the ultrasound diagnostic device pertaining to embodiment2. The receive beam former 104A pertaining to embodiment 2 includes adelay-and-sum calculator 1041A. For each transmission event, thedelay-and-sum calculator 1041A sets a target area composed of twopartial areas of differing type, and further, generates a sub-frameacoustic line signal for each partial area. In addition, the receivebeam former 104A pertaining to embodiment 2 includes a synthesizer1140A. The synthesizer 1140A combines sub-frame acoustic lines generatedfrom partial areas of the same type to generate a frame part acousticline signal for each type of partial area. Further, the synthesizer1140A generates a frame acoustic line signal by combining the frame partacoustic line signals of the two partial area types. Other than thedelay-and-sum calculator 1041A and the synthesizer 1140A, the componentsof the ultrasound diagnostic device pertaining to embodiment 2 have thesame structures and configurations as the corresponding components inthe ultrasound diagnostic device 100 described in embodiment 1. Thus,description of such similar components is not provided in the following.

(1) Delay-and-Sum Calculator 1041A

The delay-and-sum calculator 1041A includes a target area setter that,for each transmission event, sets a target area Bx based on theinformation indicating the position of the transmission aperture Tx forthe transmission event, which is acquired from the transmission beamformer 103.

FIG. 18 is a schematic illustrating one target area Bx. As illustratedin FIG. 18, the target area Bx includes two partial areas. One is aprimary partial area Bx1, which corresponds to the inside of theultrasound main irradiation area Ax. The other is a secondary partialarea Bx2, which is the area of the target area Bx that is outside theultrasound main irradiation area Ax. The secondary partial area Bx2 isadjacent to at least one side of the primary partial area Bx1 in thetransducer element array direction. The target area Bx, as a whole, isset so that the minimum width Wf thereof in the transducer element arraydirection is equal to or greater than the shift amount Mp. This issimilar to embodiment 1. Meanwhile, in the present embodiment, eachtarget area Bx is a combination of the two types of partial areasdescribed above, i.e., a primary partial area Bx1 and a secondarypartial area Bx2. The following describes the relationship between theprimary partial area Bx1 and the secondary partial area Bx2. Thesecondary partial area Bx2 is a combination of two triangular areas bothhaving the transmission focal point F as one vertex thereof. The widthof the secondary partial area Bx2 in the transducer element arraydirection is set so that, at a depth where the width of the primarypartial area Bx1 is smaller than the minimum width Wf, the sum of thewidth of the secondary partial area Bx2 and the width of the primarypartial area Bx1 equals the minimum width Wf. For example, when theshift amount Mp is equal to eight times the width of a single transducerelement, the minimum width Wf may be equal to or greater than ten timesthe width of a single transducer element. Further, it is preferable thattwo secondary partial areas Bx2 respectively corresponding to twoconsecutive transmission events (i.e., two secondary partial areas Bx2differing in position by the shift amount Mp) overlap one another by atleast 50%. This configuration is preferable since, increasing the amountof overlap between two secondary partial areas Bx2 respectivelycorresponding to two consecutive transmission events increases thenumber of measurement points having overlap counts of at least two, andthus, ultrasound image quality increases at areas corresponding to suchsecondary partial areas Bx2. When set in such a manner, the target areaBx includes both measurement points covering substantially the entireultrasound main irradiation area Ax and measurement points located inthe proximity of the ultrasound main irradiation area Ax, which achievesefficient use of transmitted ultrasound.

For each of the measurement points Pij included in the target area Bxset for a given transmission event, the delay-and-sum calculator 1041Aperforms delay-and-sum processing with respect to receive signalsequences for the measurement point Pij, each of which is received byone of the receive transducer elements Rk. Thus, the delay-and-sumcalculator 1041A calculates an acoustic line signal for each measurementpoint Pij included in the target area Bx, and generates a sub-frameacoustic line signal.

Here, it should be noted that for each transmission event, thedelay-and-sum calculator 1041A pertaining to embodiment 2 generates aprimary sub-frame acoustic line signal covering ones of the measurementpoints Pij included in the primary partial area Bx1 and a secondarysub-frame acoustic line signal covering ones of the measurement pointsPij included in the secondary partial area Bx2. Further, thedelay-and-sum calculator 1041A outputs the primary sub-frame acousticline signal and the secondary sub-frame acoustic line signal to bestored in the data storage 107.

(2) Synthesizer 1140A

For each transmission event, the synthesizer 1140A generates one signal(introduced in the following as a primary frame part acoustic linesignal) from primary sub-frame acoustic line signals corresponding tomultiple transmission events, and one signal (introduced in thefollowing as a secondary frame part acoustic line signal) from secondarysub-frame acoustic line signals corresponding to multiple transmissionevents. The synthesizer 1140A includes two adders (an adder 11401A-1 andan adder 11401A-2), two amplifiers (an amplifier 11402A-1 and anamplifier 11402A-2), and a combiner 11403A.

Each of the adders 11401A-1 and 11401A-2, when a series of sub-frameacoustic line signals of the corresponding type (i.e., primary sub-frameacoustic line signals for the adder 11401A-1, and secondary sub-frameacoustic line signals for the adder 11401A-2) necessary for generatingone frame acoustic line signal have been generated, reads out thesub-frame acoustic line signals of the corresponding type from the datastorage 107. Further, each of the adders 11401A-1 and 11401A-2 combinesthe sub-frame acoustic line signals of the corresponding type accordingto the positions of the measurement points Pij from which the acousticline signals included in the sub-frame acoustic line signals of thecorresponding type are acquired. In the present embodiment, the adder11401A-1 generates a primary combined acoustic line signal by combiningmultiple primary sub-frame acoustic line signals, and the adder 11401A-2generates a secondary combined acoustic line signal by combiningmultiple secondary sub-frame acoustic line signals. Thus, in the presentembodiment, the term combined acoustic line signal refers to either theprimary combined acoustic line signal or the secondary combined acousticline signal. Further, note that that even if both the primary sub-frameacoustic line signal and the secondary sub-frame acoustic line signalinclude signals for a same measurement point Pij, the combining of suchsignals for the same measurement point is not performed.

FIGS. 19A through 19C are schematics illustrating processing ofgenerating a frame acoustic line signal from the primary and secondarysub-frame acoustic line signals. FIG. 19A illustrates the processing ofcombining a plurality of primary sub-frame acoustic line signalsaccording to the positions of measurement points P to generate a primarycombined acoustic line signal covering all primary partial areas Bx1.Meanwhile, FIG. 19B illustrates the processing of combining a pluralityof secondary sub-frame acoustic line signals according to the positionsof measurement points P to generate a secondary combined acoustic linesignal covering all secondary partial areas Bx2.

The amplifier 11402A-1 performs amplification processing of amplifyingthe primary combined acoustic line signal by using amplification factorseach of which is determined based on the number of acoustic linesignals, included in the primary sub-frame acoustic line signals,combined to yield the primary combined acoustic line signal. Similarly,the amplifier 11402A-2 performs amplification processing of multiplyingthe secondary combined acoustic line signal by using amplificationfactors each of which is determined based on the number of acoustic linesignals, included in the secondary sub-frame acoustic line signals,combined to generate the secondary combined acoustic line signal.Further, each of the amplifiers 11402A-1 and 11402A-2 may also multiplythe corresponding combined acoustic line signal by amplification factorsvarying in the transducer element array direction that are calculatedbased on overlap counts, when overlap counts vary in the transducerelement array direction. This moderates a difference between values ofthe corresponding combined acoustic line signal deriving from thedifference in overlap counts in the transducer element array direction,and thus, the values of the corresponding combined acoustic line signalafter the amplification are averaged out in the transducer element arraydirection. Through such amplification, the primary combined acousticline signal becomes a primary frame part acoustic line signal, and thesecondary combined acoustic line signal becomes a secondary frame partacoustic line signal. The amplifier 11402A-1 outputs the primary framepart acoustic line signal to be stored in the data storage 107, and theamplifier 11402A-2 outputs the secondary frame part acoustic line signalto be stored in the data storage 107.

The primary frame part acoustic line signal and the secondary frame partacoustic line signal are then combined by the combiner 11403A togenerate a frame acoustic line signal.

FIG. 19C is a schematic illustrating processing of generating a frameacoustic line signal from the primary frame part acoustic line signaland the secondary frame part acoustic line signal. First in thisprocessing, for each measurement point P, a determination is made of aregion to which the measurement point P belongs. Specifically, eachmeasurement point P belongs to one of the three types of regionsdescribed in the following. A measurement point P is determined asbelonging to region 501 when the measurement point P is included in aprimary partial area Bx1 for at least one transmission event and is notincluded in a secondary partial area Bx2 for any transmission event. Ameasurement point P is determined as belonging to region 502 when themeasurement point P is included in a secondary partial area Bx2 for atleast one transmission event and is not included in a primary partialarea Bx1 for any transmission event. A measurement point P is determinedas belonging to region 503 when the measurement point P is included in aprimary partial area Bx1 for at least one transmission event and is alsoincluded in a secondary partial area Bx2 for at least one transmissionevent. Further, for a measurement point P belonging to region 501, avalue of a corresponding acoustic line signal in the primary frame partacoustic line signal is included in the frame acoustic line signal. Fora measurement point P belonging to region 502, a value of acorresponding acoustic line signal in the secondary frame part acousticline signal is included in the frame acoustic line signal. For ameasurement point P belonging to region 503, a value of a correspondingacoustic line signal included in the primary frame part acoustic linesignal and/or a value of a corresponding acoustic line signal in thesecondary frame part acoustic line signal is/are used for calculating avalue of an acoustic line signal included in the frame acoustic linesignal corresponding to the measurement point P. However, note that inthe present embodiment, for a measurement point P belonging to region503, only a value of a corresponding acoustic line signal in the primaryframe part acoustic line signal is included in the frame acoustic linesignal. Such a configuration achieves, for each measurement point Pbelonging to region 503, calculating a value of a corresponding acousticline signal included in the frame acoustic line signal by using onlyacoustic line signal values having been acquired when the measurementpoint P was inside ultrasound main irradiation areas Ax. Thus, thisconfiguration achieves high spatial resolution and high signal S/N ratiofor measurement points belonging to region 503, as well as formeasurement points belonging to region 501.

Nevertheless, for a measurement point P belonging to region 503, both avalue (first value) of a corresponding acoustic line signal included inthe primary frame part acoustic line signal and a value (second value)of a corresponding acoustic line signal in the secondary frame partacoustic line signal may be used for calculating a value (third value)of a corresponding acoustic line signal included in the frame acousticline signal. In this case, the third value may be acquired bycalculating an arithmetic mean, a geometric mean, or a linearcombination of the first and second values. Calculating the third valueby using both the first and second values prevents the risk of aconsiderable gap occurring in the frame acoustic line signal, betweenvalues corresponding to measurement points at both sides of a boundarybetween regions 501 and 503. This ensures sufficient image qualityimprovement at such a boundary.

The frame acoustic line signal so generated is output by the combiner11403A to be stored in the data storage 107.

<Operations>

FIG. 20 is a flowchart illustrating beam forming by the receive beamformer 104A. The flowchart of FIG. 20 differs from the flowchart of FIG.11 for: (i) including Step S210A in place of Step S210 (target areasetting); (ii) including Step S220A, which includes Step S224A, in placeof Step S220 (receive beam focusing), which includes Step S224 (acousticline signal generating); (iii) including Step S501 in place of Step S301(frame acoustic line signal generating); and (iv) including Step S502 inplace of Step S302 (frame acoustic line signal amplification), and forfurther including Step S503 not included in FIG. 11. Meanwhile, theprocessing in steps other than such steps in the flowchart in FIG. 20 issimilar to the processing in the corresponding steps in the flowchart inFIG. 11. Thus, description of such similar processing is not provided inthe following.

In Step S210A, the target area setter of the delay-and-sum calculator1041A sets a target area Bx for the processing-target transmissionevent. In specific, the target area setter, based on the informationindicating the position of the transmission aperture Tx for thetransmission event, sets a primary partial area Bx1 and a secondarypartial area Bx1.

Subsequently, processing proceeds to measurement-point dependent beamforming in Step S220A (including Steps S221 through S223, Step S224A,and Steps S225 through S228). Since the processing in Step S220A, otherthan the processing in Step S224A, is similar to the correspondingprocessing in Step S220, only the processing in Step S224A is describedin the following.

In Step S224A, the delay-and-sum calculator 1041A generates an acousticline signal for the processing-target measurement point Pij, and outputsthe acoustic line signal so generated to the data storage 107. Here,when the measurement point Pij is included in the primary partial areaBx1, the delay-and-sum calculator 1041A includes the acoustic linesignal for the measurement point Pij in the primary sub-frame acousticline signal, which is output to the data storage 107. Meanwhile, whenthe measurement point Pij is included in the secondary partial area Bx2,the delay-and-sum calculator 1041A includes the acoustic line signal forthe measurement point Pij in the secondary sub-frame acoustic linesignal, which is output to the data storage 107. Through the processingin Step S220A being repeated, the primary sub-frame acoustic line signalcorresponding to the primary partial area Bx1 and the secondarysub-frame acoustic line signal corresponding to the secondary partialarea Bx2 are generated.

Subsequently, a determination is performed of whether or not a set of aprimary sub-frame acoustic line signal and a secondary sub-frameacoustic line signal has been generated for each transmission eventhaving been performed (Step S230). When the set of sub-frame acousticsignals has not yet been generated for one or more transmission events,processing returns to Step S210A, where the target area setter sets atarget area Bx (i.e., a primary partial area Bx1 and a secondary partialarea Bx2) for the subsequent transmission event based on informationindicating the transmission aperture Tx for the subsequent transmissionevent, which is acquired from the transmission beam former 103 (StepS210A). Meanwhile, when the set of sub-frame acoustic line signals hasbeen generated for all transmission events, processing proceeds to StepS501.

Subsequently, a primary combined acoustic line signal is generated bycombining primary sub-frame acoustic line signals according to thepositions of the measurement points Pij, and a secondary combinedacoustic line signal is generated by combining secondary sub-frameacoustic line signals according to the positions of the measurementpoints Pij (Step S501). Then, the primary combined acoustic line signaland the secondary combined acoustic line signal are each multiplied byamplification factors that are in accordance with the number of signalscombined to generate the signal, whereby a primary frame part acousticline signal and a secondary frame part acoustic line signal arerespectively generated (Step S502). Further, the primary frame partacoustic line signal and the secondary frame part acoustic line signalare combined, to generate a frame acoustic line signal (Step S503).Subsequently, the frame acoustic line signal so generated is output tothe ultrasound image generator 105 and the data storage 107 (Step S303).This completes the processing.

<Effects>

As described up to this point, the ultrasound diagnostic devicepertaining to embodiment 2, similar to the ultrasound diagnosticapparatus 100 pertaining to embodiment 1, prevents the occurrence ofdefective areas even when the shift amount is provided with a greatvalue. Thus, the ultrasound diagnostic device pertaining to embodiment 2prevents image quality reduction while achieving high frame rate. FIG.26A illustrates one example of an ultrasound image generated by theultrasound diagnostic device pertaining to embodiment 2. The ultrasoundimage in FIG. 26A does not have defective areas (i.e., areas where datais missing). Thus, vertical stripes at the transmission focal depth areless prominent in the ultrasound image in FIG. 26A than in theultrasound image in FIG. 26D.

In addition, the ultrasound diagnostic device pertaining to embodiment 2separately performs (i) the combining of primary partial areas Bx1 and(ii) the combining of secondary partial areas Bx2, and then combines theresult of the combining in (i) and the result of the combining in (ii).Further, the ultrasound diagnostic device pertaining to embodiment 2,for a measurement point Pij for which an acoustic line signal in theframe acoustic line signal can be generated by combining signalscorresponding thereto that are included in primary sub-frame acousticline signals, does not use signals corresponding thereto that areincluded in secondary sub-frame acoustic line signals for generating theframe acoustic line signal. The frame acoustic line signal, due toincluding an acoustic line signal based on only the primary sub-frameacoustic line signals for such a measurement point P, has improvedspatial resolution and signal S/N ratio where corresponding to such ameasurement point P.

<<Modification 2>>

The delay-and-sum calculator 1041A of the ultrasound diagnostic devicepertaining to embodiment 2 calculates a transmission time for eachmeasurement point included in primary partial areas Bx1 and atransmission time for each measurement point included in secondarypartial areas Bx2 in the same manner.

Meanwhile, modification 2 describes a delay-and-sum calculator includinga transmission time calculator that changes the method used for thecalculation of transmission times depending upon whether a measurementpoint Pij is included in a primary partial area Bx1 or a secondarypartial area Bx2.

<Calculation of Transmission Times>

The following describes the method used in the present modification forthe calculation of transmission times, with reference to FIGS. 21Athrough 21D. Each of FIGS. 21A and 21B is a schematic illustratingpropagation paths of ultrasound according to the present modification.In the present modification, the calculation of a transmission time foreach measurement point Pij included in a primary partial area Bx1 isconducted according to the method described with reference to FIGS. 7Aand 7B. That is, a transmission time for such a measurement point Pij iscalculated such that (i) when the measurement point Pij is located at ordeeper than the transmission focal depth, a sum of the time amountrequired for transmitted ultrasound to travel through path 401 and thetime amount required for transmitted to travel through path 402 is usedas the transmission time, and (ii) when the measurement point Pij islocated shallower than the transmission focal depth, a value obtained bysubtracting the time amount required for transmitted ultrasound totravel through path 402 from the time amount required for transmittedultrasound to travel through the path 401 is used as the transmissiontime.

Meanwhile, in the present modification, the calculation of atransmission time for each measurement point Pij included in a secondarypartial area Bx2 is conducted according to a method differing from themethod described with reference to FIGS. 7A and 7B. To begin with,description is provided why the present modification differentiates thecalculation method of transmission times between measurement points Pijincluded in primary partial areas Bx1 and measurement points Pijincluded in secondary partial areas Bx2, with reference to FIGS. 22Athrough 22C. FIG. 22A illustrates a case where the calculation methodapplied to measurement points included in primary partial areas Bx1 isalso applied to measurement points included in secondary partial areasBx2. FIG. 22A shows line 613 that is straight and perpendicular to thetransducer element array direction along which the transducer elements101 a are disposed. Point B indicates a point along line 613 that islocated at the transmission focal depth Df. In the case illustrated inFIG. 22A, for measurement point P1 located deeper than the transmissionfocal depth Df, a sum of the time amount required for transmittedultrasound to travel through path 401 and the time amount required fortransmitted to travel through path 4021 is used as the transmission timefor measurement point P₁, and for measurement point P₂ located shallowerthan the transmission focal depth Df, a value obtained by subtractingthe time amount required for transmitted ultrasound to travel throughpath 4022 from the time amount required for transmitted ultrasound totravel through path 401 is used as the transmission time for themeasurement point P₂. Note that the transmission time for point B may becalculated according to either the calculation method applied formeasurement points located deeper than the transmission focal depth Dfor the calculation method applied to measurement points locatedshallower than the transmission focal depth Df. Here, if supposing thatthe points P₁, B, and P₂ are very close to one another, the distancebetween points B and F (i.e., the transmission focal point), the lengthof path 4021, and the length of path 4022 would be substantially equal.Despite this situation, applying the different calculation methodsdescribed above to points P₁ and P₂ results in the transmission timesfor points P₁ and P₂ differing by a time amount of 2×(distance betweenpoints B and F)/(ultrasound velocity in subject). Further, thisdifference changes depending upon the distance between points B and F,and in particular, the greater the distance between points B and F, thegreater this difference. This difference in transmission time betweenpoints P₁ and P₂ results in a discontinuity, at the transmission focaldepth Df, in the change of transmission times in the depth direction.FIG. 22B illustrates, for measurement points Pij along line 613, arelationship between the depths D of the measurement points Pij and thetransmission times calculated for the measurement points Pij whenapplying the different calculation methods described above to points P₁and P₂. FIG. 22B clearly shows this discontinuity, at the transmissionfocal depth Df, in the change of transmission times in the depthdirection. Naturally, this discontinuity results in a similardiscontinuity, at the transmission focal depth Df, between delay amountsto be applied to the measurement points Pij in the delay-and-sumprocessing. Meanwhile, FIG. 22B illustrates a case where thetransmission time for point B located at focal depth Df is calculatedaccording to the calculation method applied to measurement pointslocated deeper than the transmission focal depth Df. However, even ifthe transmission time for point B were calculated according to thecalculation method applied to measurement points located shallower thanthe transmission focal depth Df, a similar discontinuity in the changeof transmission times in the depth direction would occur at thetransmission focal depth Df, while a different value would be calculatedas the transmission time for point B. (This case can be depicted byreplacing the unfilled circle with a filled circle and replacing thefilled circle with an unfilled circle in FIG. 22B.) This discontinuity,at the transmission focal depth Df, in the change of transmission timesin the depth direction (and the consequent discontinuity, at thetransmission focal depth Df, in the change of delay amounts in the depthdirection) results in a discontinuity, at the transmission focal depthDf, of measurement point values of a secondary sub-frame acoustic linesignal. This further results in, for example, noise appearing in a frameacoustic line signal along the transmission focal depth. This means thatthere remains room for further image quality improvement with respect toregion 502. For example, as can be seen in the ultrasound image shown inFIG. 22C, a difference in luminance may be present between areascorresponding to secondary sub-frame acoustic line signals that arelocated at opposite sides of the transmission focal depth Df (e.g.,between area 5021 and area 5022 in FIG. 22C). Eliminating such adifference in luminance would improve image quality.

In view of this, in the present modification, transmissions time formeasurement points Pij included in secondary partial areas Bx2 arecalculated as described in the following. FIG. 21A illustrates onemethod applicable in the calculation of transmission times formeasurement points Pij included in secondary partial areas Bx2. Atransmission time calculated according to the method illustrated in FIG.21A is denoted as a transmission time T_(D) in the following. In thismethod, the calculation of a transmission time for a measurement pointPij included in a secondary partial area Bx2 is performed regarding thattransmitted ultrasound from the transmission aperture Tx directlyreaches the measurement point Pij by traveling along path 601. That is,transmission time T_(D) is the time amount required for ultrasoundtransmitted from a center position of a transmission aperture Tx toarrive at a measurement point Pij by traveling through path 601. FIG.21C corresponds to the method illustrated in FIG. 21A, and illustrates,for measurement points Pij along line 611 that is straight andperpendicular to the transducer element array direction, a relationshipbetween depths D of the measurement points Pij and the transmissiontimes T_(D) calculated for the measurement points Pij.

As illustrated in FIG. 21C, transmission time T_(D) increasesmonotonically as depth D increases, and thus, there is no discontinuitybetween the transmission times for the measurement points Pij along line611.

Further, FIG. 21B illustrates another method applicable in thecalculation of transmission times for measurement points included insecondary partial areas Bx2. A transmission time calculated according tothe method illustrated in FIG. 21B is denoted as a transmission timeT_(S) in the following. In this method, the calculation of atransmission time for a measurement point Pij included in a secondarypartial area Bx2 is performed by using path 602 that is the shortestamong paths connecting the transmission aperture Tx and a referencepoint R at the same depth as the measurement point Pij, regarding thattransmitted ultrasound from the transmission aperture Tx reaches themeasurement point Pij and the reference point R at the same time. Thatis, transmission time T_(S) is the time amount required for ultrasoundtransmitted from a center position of a transmission aperture to arriveat a reference point R by traveling through path 602. Here, note thatpath 602 has the same length as path 603 connecting the transducerelement spatially closest to the measurement point Pij to themeasurement point Pij, which is the shortest among paths connecting thetransmission aperture Tx and the measurement point Pij. In other words,path 602 has a length equal to the depth of the measurement point Pij.FIG. 21D corresponds to the method illustrated in FIG. 21B, andillustrates, for measurement points Pij along line 612 that is straightand perpendicular to the transducer element array direction, arelationship between depths D of the measurement points Pij and thetransmission times T_(S) calculated for the measurement points Pij. Asillustrated in FIG. 21D, transmission time T_(S) increases monotonicallyas depth D increases, and thus, there is no discontinuity between thetransmission times for the measurement points Pij along line 613.

Further, note that transmissions time for measurement points Pijincluded in secondary partial areas Bx2 may be calculated according tomethods other than those described above, as long as for measurementpoints Pij along a straight line perpendicular to the transducer elementarray direction, transmission time monotonically increases as depthincreases. For example, a transmission time for a measurement point Pijincluded in a secondary partial area Bx2 may be calculated based on apath connecting any single position of a transmission aperture Tx and anany single point at the same depth as the measurement point Pij.

Calculating transmission times for measurement points Pij included insecondary partial areas Bx2 as described above achieves the followingeffects: (i) the effect described in embodiment 1 of preventing theoccurrence of defective areas even when the shift amount is providedwith a great value, and thereby preventing image quality reduction whileachieving high frame rate; (ii) the effect described in embodiment 2 ofpreventing a decrease in spatial resolution and signal S/N ratio thatwould otherwise occur when using, for a measurement point Pij for whichan acoustic line signal in the frame acoustic line signal can begenerated by combining only signals corresponding thereto that areincluded in primary sub-frame acoustic line signals, signalscorresponding thereto that are included in both primary sub-frameacoustic line signals and secondary sub-frame acoustic line signals forgenerating a frame acoustic line signal; and (iii) an effect ofimproving ultrasound image quality as illustrated by the exampleultrasound image shown in FIG. 26B, by preventing a discontinuity intransmission time at the transmission focal depth.

<<Modification 3>>

The delay-and-sum calculator pertaining to modification 2 calculates atransmission time for a measurement point Pij included in a secondarypartial area Bx2 based on a path connecting any single position of atransmission aperture Tx and any single point at the same depth as themeasurement point Pij.

However, completely differentiating the calculation method oftransmission times between measurement points Pij included in primarypartial areas Bx1 and measurement points Pij included in secondarypartial areas Bx2 results in a discontinuity in transmission timesoccurring at a boundary between a primary partial area Bx1 and asecondary partial area Bx2. This further results in, for example, noiseappearing along a boundary between region 501 and region 502. This meansthat image quality improvement at the boundary between region 501 andregion 502 is insufficient. FIG. 23D is a schematic showing anultrasound image including noise at a boundary between area 5012corresponding to primary sub-frame acoustic line signals and area 5022corresponding to secondary sub-frame acoustic line signals.

In view of this, a delay-and-sum calculator pertaining to modification 3calculates transmission times for measurement points Pij included insecondary partial areas Bx2 so that there is no discontinuity intransmission time between primary partial areas Bx1 and secondarypartial areas Bx2, and transmission time increases monotonically asdepth increases.

<Calculation of Transmission Times>

The following describes the method used in the present modification forthe calculation of transmission times for measurement points Pijincluded in secondary partial areas Bx2, with reference to FIGS. 23Athrough 23D. FIG. 23A is a schematic illustrating propagation paths ofultrasound according to the present modification. FIG. 23A shows line610 that is straight and perpendicular to the transducer element arraydirection. In the present modification, transmission times formeasurement points R₁ and R₃ (respectively referred to in the followingas boundary points R₁ and R₃), each of which is located at a boundarybetween a secondary partial area Bx2 and a primary partial area Bx1, arecalculated according to the method applied in the calculation oftransmission times for measurement points Pij included in primarypartial areas Bx1. In specific, the transmission time for boundary pointR₁ located deeper than the transmission focal depth is calculated bysumming the time amount required for transmitted ultrasound to travelthrough path 401 and the time amount required for transmitted ultrasoundto travel through path 4021. Meanwhile, the transmission time forboundary point R₃ located shallower than the transmission focal depth iscalculated by subtracting the time amount required for transmittedultrasound to travel through path 4022 from the time amount required fortransmitted ultrasound to travel through path 401.

Meanwhile, the transmission time for measurement point R₂ (referred toin the following as intermediate point R₂), which is located along line610, is located at the transmission focal depth Df, and is locatedhalfway between the boundary points R₁ and R₃, is calculated accordingto the method illustrated in FIG. 21A. That is, the time amount requiredfor transmitted ultrasound to travel through path 6011 (i.e.,transmission time T_(D)) is regarded as the transmission time forintermediate point R₂.

Further, in the present modification, for each measurement point Pijlocated between boundary point R₁ and intermediate point R₂ and for eachmeasurement point Pij located between boundary point R₃ and intermediatepoint R₂, a transmission time is calculated by using both a transmissiontime for the measurement point Pij that is calculated according to themethod applied to measurement points included in primary partial areasBx1 (denoted in the following as transmission time T_(R)) and atransmission time T_(D) calculated for the measurement point Pij. Here,note that a transmission time T_(S) calculated for the measurement pointPij may be used in place of the transmission time T_(D) calculated forthe measurement point Pij. Note that the following description isprovided based on a case where the transmission time T_(D) calculatedfor the measurement point Pij is used in combination with a transmissiontime T_(R) calculated for the measurement point Pij. However, thefollowing description similarly applies to when the transmission timeT_(S) calculated for the measurement point Pij is used in place of thetransmission time T_(D) calculated for the measurement point Pij.

Specifically, in calculating transmission times for measurement pointsPij located between boundary point R₁ and intermediate point R₂ andmeasurement points Pij located between boundary point R₃ andintermediate point R₂, a transmission time for each of the measurementpoints Pij is calculated by combining the transmission time T_(R) andthe transmission time T_(D) for the measurement point Pij so that thefollowing conditions are satisfied. Condition (1): The transmissiontimes for the measurement points Pij monotonically increase as depth Dincreases, without any discontinuity therebetween. Condition (2): Foreach boundary point (R₁ and R₃), the transmission time T_(R) calculatedfor the boundary point is used as the transmission time for the boundarypoint. Condition (3): For intermediate point R₂, the transmission timeT_(D) calculated for intermediate point R₂ is used as the transmissiontime for intermediate point R₂. FIG. 23B is a graph illustrating, formeasurement points Pij located between boundary point R₁ andintermediate point R₂ and measurement points Pij located betweenboundary point R₃ and intermediate point R₂, a relationship betweendepths D and transmission times for such measurement points Pij. In FIG.23B, line 701 indicates transmission times T_(R) calculated for themeasurement points Pij, and line 702 indicates transmission times T_(D)calculated for the measurement points Pij. For example, in the presentmodification, transmission times for measurement points Pij locatedbetween boundary point R₁ and intermediate point R₂ and measurementpoints Pij located between boundary point R₃ and intermediate point R₂are calculated such that the depths D and the transmission times forsuch measurement points Pij satisfy the relationship indicated by line703 in FIG. 23B, which is a straight line connecting the intercept ofline 701 at depth D₂ and the intercept of line 701 at depth D₁. However,the calculation of transmission times of measurement points Pij locatedbetween the boundary point R₁ and the intermediate point R₂ andmeasurement points Pij located between the boundary point R₃ and theintermediate point R₂ need not be performed so that the transmissiontimes satisfy the specific relationship indicated by line 703 in FIG.23B, as long as the transmission times satisfies a relationship thatwould satisfy the following conditions based on FIG. 23B. Condition (i):A line representing the transmission times for such measurement pointsPij intersects line 701 at both depths D₁ and D₂. Condition (ii): Theline representing the transmission times for such measurement points Pijdoes not have any discontinuity between depth D₂ and depth D₁. Condition(iii): The line representing the transmission times for such measurementpoints Pij monotonically increases (rises to the right) from depth D₂ todepth D₁. Note that in FIGS. 23A through 23C, depth D₁ is depth D forboundary point R₁, and depth D₂ is depth D for boundary point R₃.

For example, transmission times of such measurement points Pij may becalculated by using linear combination. When using linear combination, atransmission time for each of such measurement points (denoted in thefollowing as transmission time T_(M)) satisfies the following equation.T _(M) =αT _(R)+(1−α)T _(D)

Here, α satisfies the two following conditions. Condition (4): α=0 whenD=D_(f), where D_(f) denotes the depth D for intermediate point R₂ inFIGS. 23A through 23C. Condition (5) α=1 when D=D₁ or D=D₂. For example,when supposing that α is proportional to |D−D_(f)|, a can be defined bythe following equation.α=|D−D _(f)|/(D ₁ −D _(f))

When α is defined by this equation, the relation between α and thedepths of the measurement points Pij located between the boundary pointsR₁ and R₃ and the intermediate point R₂ can be depicted by a combinationof two straight lines 711, one between D₂ and D_(f) and the otherbetween D_(f) and D₁, in FIG. 23C. Note that α need not be defined bythe equation above, and α may for example take values representable bycurves 712 and curves 713 in FIG. 23C, as long as transmission timeT_(M) satisfies Conditions (1) through (5) discussed above.

In addition, note that transmission time T_(M) need not be calculated byusing linear combination as described above, and may be calculated byother methods as long as transmission time T_(M) satisfies Conditions(1) through (3) discussed above. For example, transmission time T_(M)may be defined by the following equation.T _(M) =T _(R) ^(α) ×T _(D) ^((1-α))

Needless to say, substituting T_(S) for T_(D) in this equation is alsopossible. Further, in any equation provided in the present modification,any transmission time that satisfies the condition provided inmodification 2 that transmission times for measurement points Pij alonga straight line perpendicular to the transducer element array directionmonotonically increase as depth increases, without any discontinuitytherebetween, may be substituted for transmission time T_(D). Oneexample of such a transmission time is a transmission time calculatedbased on any path connecting one position of the transmission apertureTx to one point at the same depth as the measurement point Pij.

Transmission times T_(M) as described above monotonically increase asdepth increases, without any discontinuity. As a result, the change invalues of acoustic line signals for measurement points Pij in the depthdirection becomes smooth, without any discontinuity. FIG. 26Billustrates one example of an ultrasound image generated by employingthe calculation method of transmission times pertaining to the presentmodification. The present modification, as well as achieving the effectsof modification 2, achieves further image quality improvement at thetransmission focal depth and at boundaries between primary partial areasBx1 and secondary partial areas Bx2, by ensuring that the change intransmission time in the depth direction is continuous.

<<Modification 4>>

As described above, the target area setter of the delay-and-sumcalculator 1041A pertaining to embodiment 2 sets, for each transmissionevent, a target area Bx including a primary partial area Bx1 and asecondary partial area Bx2. Further, in embodiment 2, the primarypartial area Bx1 and the secondary partial area Bx2 do not overlap eachother.

Meanwhile, in the present modification, a target area Bx for eachtransmission event includes a primary partial area Bx1 and a secondarypartial area Bx2, and the primary partial area Bx1 and the secondarypartial area Bx2 overlap one another.

<Setting of Target Area Bx>

The following describes how a target area Bx is set in the presentmodification, and how a primary frame part acoustic line signal and asecondary frame part acoustic line signal are combined in the presentmodification.

FIG. 24A is a schematic illustrating a target area Bx pertaining to thepresent modification. The present modification is similar to embodiment2 in that the primary partial area Bx1 corresponds to the inside of theultrasound main irradiation area Ax. Further, the present modificationis similar to embodiment 2 in that the secondary partial area Bx2 is setso that the minimum Wf of the overall width of the target area Bx is nosmaller than the shift amount Mp. Meanwhile, the present modificationdiffers from embodiment 2 in that the secondary partial area Bx2 has arectangular shape and partially overlaps the primary partial area Bx1.That is, the secondary partial area Bx2 pertaining to the presentmodification is a combination of the secondary partial area Bx2pertaining to embodiment 2 and a part of the primary partial area Bx1pertaining to embodiment 2.

Similar to embodiment 2, for each of the measurement points Pij includedin the target area Bx set for a given transmission event, thedelay-and-sum calculator 1041A performs delay-and-sum processing withrespect to receive signal sequences for the measurement point Pij, eachof which is received by one of the receive transducer elements Rk. Thus,the delay-and-sum calculator 1041A calculates an acoustic line signalfor each measurement point Pij included in the target area Bx, andgenerates a sub-frame acoustic line signal.

Further, similar to embodiment 2, sub-frame acoustic line signals ofeach type (primary sub-frame acoustic line signals and secondarysub-frame acoustic line signals) are combined according to the positionsof the measurement points Pij from which the acoustic line signalsincluded in the sub-frame acoustic line signals are acquired. Further,similar to embodiment 2, amplification processing of amplifying theprimary combined acoustic line signal by using amplification factorseach determined based on the number of acoustic line signals, includedin primary sub-frame acoustic line signals, combined to generate theprimary combined acoustic line signal is performed. Similarly,amplification processing of multiplying the secondary combined acousticline signal by using amplification factors each determined based on thenumber of acoustic line signals, included in secondary sub-frameacoustic line signals, combined to generate the secondary combinedacoustic line signal is performed. Through such amplification, theprimary combined acoustic line signal becomes a primary frame partacoustic line signal, and the secondary combined acoustic line signalbecomes a secondary frame part acoustic line signal. The primary framepart acoustic line signal and the secondary frame part acoustic linesignal are then combined to generate a frame acoustic line signal.

FIG. 24B is a schematic pertaining to the present modificationillustrating processing of generating a frame acoustic line signal fromthe primary frame part acoustic line signal and the secondary frame partacoustic line signal. Similar to embodiment 2, for each measurementpoint P, a determination is made of a region (region 501, region 502, orregion 503) to which the measurement point P belongs. For a measurementpoint P belonging to region 501 or region 503, a value of acorresponding acoustic line signal in the primary frame part acousticline signal is included in the frame acoustic line signal. Meanwhile,for a measurement point P belonging to region 502, a value of acorresponding acoustic line signal in the secondary frame part acousticline signal is included in the frame acoustic line signal. Here, notethat in the present modification, for a measurement point P belonging toregion 503, only a value of a corresponding acoustic line signal in theprimary frame part acoustic line signal is included in the frameacoustic line signal. This is since, for a measurement point P locatedwhere the secondary partial area Bx2 overlaps a part of the primarypartial area Bx1, using a corresponding acoustic line signal in theprimary frame part acoustic line signal, which was acquired when themeasurement point P was included in primary partial areas Bx1, achieveshigher spatial resolution and higher signal S/N ratio compared to usinga corresponding acoustic line signal in the secondary frame partacoustic line signal.

As such, secondary partial areas Bx2 pertaining to the presentmodification, as well as achieving the effects described in embodiment2, has a simpler shape than secondary partial areas Bx2 pertaining toembodiment 2. Due to this, setting secondary partial areas Bx2 asdescribed in the present modification simplifies the computationrequired in generating secondary sub-frame acoustic line signals and thesecondary frame part acoustic line signal.

<<Other Modifications>>

(1) While description is provided in each of the embodiments andmodifications that the shift amount Mp is equal to or greater than twicethe width of a single transducer element in the transducer element arraydirection, the shift amount Mp need not have such a size. For example,the shift amount Mp may equal the width of single transducer element inthe transducer element array direction. Even when making such amodification, the width of the target area Bx in the transducer elementarray direction may be equal to or greater than the shift amount Mp,which means that the width of the target area Bx is no smaller than thewidth of a single transducer element in the transducer element arraydirection. Meanwhile, providing the shift amount Mp with such a sizeleads to target areas Bx corresponding to two consecutive transmissionevents overlapping one another without any gap therebetween. Due tothis, even when providing the shift amount Mp with such a size, theoverlap count for measurement points corresponding to where the twotarget areas Bx overlap increases, compared to a configuration whereeach target area only includes the ultrasound main irradiation area Ax.Accordingly, this modification also achieves image quality improvementin areas of ultrasound images corresponding to where two target areas Bxoverlap.

(2) While description is provided in embodiment 1 that the target areaBx includes substantially the entirety of the hourglass-shapedultrasound main irradiation area Ax, the target area Bx need not coversuch an area. For example, the target area Bx may include a part of theultrasound main irradiation area Ax and a part corresponding to theoutside of the ultrasound main irradiation area Ax. Specifically, thetarget area Bx may have a rectangular shape whose width Wf in thetransducer element array direction is equal to or greater than the shiftamount Mp. For example, as illustrated in the schematic in FIG. 25A,when the shift amount Mp equals four times the width of a singletransducer element in the transducer element array direction, therectangular target area Bx may have a width corresponding to ten timesthe width of a single transducer element in the transducer element arraydirection. Making this modification while providing the target area Bxwith a width in the transducer element array direction smaller than thewidth of the transmission aperture prevents measurement points distantfrom the ultrasound main irradiation area Ax from being included in thetarget area Bx, particularly at the transmission focal depth, and theconsequent decrease in spatial resolution and signal S/N ratio. Further,making such a modification achieves generating a frame acoustic linesignal through simple computation, as illustrated in the schematic ofFIG. 25B.

Further, the modification of setting the target area Bx to include apart of the ultrasound main irradiation area Ax and a part correspondingto the outside of the ultrasound main irradiation area Ax is applicablealso when the ultrasound main irradiation area Ax does not converge atone transmission focal point F but instead converges at a transmissionfocal area. Further, even when making this modification, modifications 2through 4 are applicable, by setting the inside of the ultrasound mainirradiation area Ax as a primary partial area Bx1 and the outside of theultrasound main irradiation area Ax as a secondary partial area Bx2.

(3) While description is provided in embodiment 2 and modifications 2through 4 that the synthesizer includes two adders and two amplifiers,the synthesizer need not have such a configuration. For example, thesynthesizer may include one adder and one amplifier, in which case theadder and the amplifier first generate a primary frame part acousticline signal from primary sub-frame acoustic line signals, and thengenerates a secondary frame part acoustic line signal from secondarysub-frame acoustic line signals.

Further, in embodiment 2 and modifications 2 through 4, thedelay-and-sum calculator may include two each of all components otherthan the target area setter, in which case the delay-and-sum calculatorperforms the generation of the primary sub-frame acoustic line signaland the generation of the secondary sub-frame acoustic line signal inparallel.

Further, in each of the embodiments and modifications, a modificationmay be made such that the delay-and-sum calculator and the synthesizerare integrated, and the following set of processing is performedsequentially for every measurement point included in the frame: (i)delay-and-sum processing for generating an acoustic line signal for themeasurement point; and (ii) combining of acoustic line signals for themeasurement point that correspond to different transmission events. Thismodification achieves direct generation of a frame acoustic line signalfrom receive signals acquired through multiple transmission eventscorresponding to one frame, or that is, generation of a frame acousticline signal without generating sub-frame acoustic lines signal eachcorresponding to one transmission event and covering the entirety of thetarget area for the corresponding transmission event. Note that evenwhen making this modification, the combining (ii) is performed after thedelay-and-sum processing (i) has been performed for each measurementpoint in the target area for each transmission event. Due to this, whilethere is a difference in whether sub-frame acoustic line signals eachcovering an entirety of a corresponding target area is generated, thecombination of processing (i) and processing (ii) is basically similarto generating a frame acoustic line signal based on sub-frame acousticline signals for the respective target areas.

(4) Up to this point, the technology pertaining to the presentdisclosure has been described based on specific embodiments andmodifications thereof. However, the embodiments and modificationsdescribed above are non-limiting examples of application of thetechnology pertaining to the present disclosure, and thus, thetechnology pertaining to the present disclosure shall be construed toencompass the following exemplar modifications.

For example, the technology pertaining to the present disclosure may beimplemented by using a computer system including a memory storing acomputer program and a microprocessor operating based on the computerprogram. For example, the computer system may store a computer programof a diagnosis method of an ultrasound diagnostic device pertaining tothe technology of the present disclosure, and the computer system mayoperate in accordance with the computer program or may provideinstructions in accordance with the computer program to variouscomponents connected thereto.

Further, the technology pertaining to the present disclosure may beimplemented by implementing a part of or the entirety of an ultrasounddiagnostic device described above, or a part of or an entirety of anbeam former described above by using a computer system including amicroprocessor, a recording medium such as a ROM or a RAM, and a harddisk unit. In this implementation, a computer program achieving the sameoperations as a device described above is stored to the RAM or the harddisk unit. Further, in this implementation, various devices achievetheir functions by the microprocessor operating in accordance with thecomputer program.

Further, the technology pertaining to the present disclosure may beimplemented by implementing some or all components included in a devicedescribed above by using one system LSI (large scale integration). Asystem LSI is an ultra-multifunctional LSI manufactured by integratingmultiple components onto one chip. Specifically, a system LSI is acomputer system including a microprocessor, a ROM, a RAM, and the like.Further, each component may be separately implemented by using one chip,or some or all components may be implemented by using one chip. Notethat LSIs are referred to by using different names, depending upon thelevel of integration achieved thereby. Such names include IC, systemLSI, super LSI, and ultra LSI. In this implementation, a computerprogram achieving the same operations as any device described above isstored to the RAM. Further, in this implementation, the system LSIachieves its functions by the microprocessor operating in accordancewith the computer program. For example, the technology pertaining to thepresent disclosure encompasses a form of implementation where an LSIstores a beam forming method pertaining to the present disclosure as aprogram, the LSI is inserted into a computer, and the computer executesthe program (i.e., the beam forming method pertaining to the presentdisclosure).

Note that integration of circuits may be achieved by a dedicated circuitor a general purpose processor, in addition to being achievable by usingan LSI as discussed above. Further, a Field Programmable Gate Array(FPGA), which is programmable after manufacturing, or a reconfigurableprocessor, which allows reconfiguration of the connection and setting ofcircuit cells inside the LSI, may be used.

Furthermore, if technology for circuit integration that replaces LSIsemerges, owing to advances in semiconductor technology or to anotherderivative technology, the integration of functional blocks maynaturally be accomplished using such technology.

Further, some or all functions of an ultrasound diagnostic devicediscussed in the embodiments may be implemented by a processor such as aCPU executing a program. Further, the technology pertaining to thepresent disclosure may be implemented by using a non-transitorycomputer-readable recording medium having recorded thereon a programcausing execution of a diagnostic method and a beam forming method of anultrasound diagnostic device. Further, execution of the program byanother independent computer system may be achieved by transferring theprogram by recording the program or a signal onto a recording medium.Naturally, the program may be distributed via means of transmissionmedia such as the internet.

Each of the ultrasound diagnostic devices pertaining to the embodimentsincludes the data storage, which is a recording device. However, therecording device need not be included in the ultrasound diagnosticdevices, and may be implemented by using a semiconductor memory, a harddisk drive, an optical disk drive, a magnetic storage device, or thelike connected to the ultrasound diagnostic devices from the outside.

Further, the functional blocks illustrated in the block diagrams aremere examples of possible functional blocks. That is, a plurality offunctional blocks illustrated in the block diagrams may be combined toform one functional block, a given functional block illustrated in theblock diagrams may be divided into a plurality of functional blocks, anda function of a given functional block illustrated in the block diagramsmay be transferred to another functional block. Further, with regards tomultiple functional blocks having similar functions, such functionalblocks may be implemented by one piece of hardware or software executingsuch functions in parallel or by applying time division.

Further, the above-described order in which steps of processing areexecuted is a non-limiting example among multiple possible orders thatis used for the sole sake of providing specific description of thetechnology pertaining to the present disclosure. Further, some of thesteps of processing described above may be executed simultaneously (inparallel).

Further, in the embodiments, description is provided that the ultrasounddiagnostic devices may have a probe and a display attached thereto.However, the ultrasound diagnostic devices may include a probe and adisplay therein.

Further, in the embodiments, the probe includes a plurality ofpiezoelectric transducer elements forming a line in one direction.However, the probe may have a different structure. For example, theprobe may include a plurality of piezoelectric transducer elementsdisposed two-dimensionally. Alternatively, the probe may be a swingableprobe including a plurality of swingable transducer elements (i.e.,transducer elements that can be caused to swing by mechanical means)forming a line in one direction, which enables acquisition ofthree-dimensional tomographic images. Further, probes of different typesmay be selected and used depending upon the examination to be performed.For example, when using a probe including piezoelectric transducerelements disposed two-dimensionally, supplying different piezoelectrictransducer elements with voltages at different timings or with voltageswith different values achieves controlling the position, the direction,etc., of the ultrasound beam to be transmitted.

Further, the probe may be provided with some of the functions of thetransmission beam former/receive beam former. For example, the probe maybe capable of generating a transmission electric signal based on acontrol signal that the transmission beam former/receive beam formeroutputs to cause generation of a transmission electric signal, and ofconverting the transmission electronic signal into ultrasound. Inaddition, the probe may be capable of converting reflected ultrasoundinto a receive electric signal, and of generating a receive signal basedon the receive electric signal.

Further, at least some of the functions of the ultrasound diagnosticdevices pertaining to the embodiments and the modifications may becombined with functions of other ones of the ultrasound diagnosticdevices pertaining to the embodiments and the modifications. Further,the values used above are non-limiting examples used for the sole sakeof providing specific description of the technology pertaining to thepresent disclosure, and may be replaced with other values.

Further, the technology pertaining to the present disclosure should beconstrued as encompassing various modifications that a skilled artisanwould arrive at based on the embodiments describe above.

SUMMARY

(1) One aspect of the present disclosure is an ultrasound signalprocessing device: performing a plurality of transmission events eachinvolving selecting a first group of transducer elements from among aplurality of transducer elements of a ultrasound probe that are arrangedin at least one line along a transducer element array direction, andcausing each transducer element in the first group to transmitultrasound towards a subject; for each of the transmission events,generating a sub-frame acoustic line signal based on ultrasoundreflection received from the subject in response to the transmissionevent, to yield a plurality of sub-frame acoustic line signals eachcorresponding to a different one of the transmission events; andgenerating a frame acoustic line signal based on the sub-frame acousticline signals for the transmission events. The ultrasound signalprocessing device includes ultrasound signal processing circuitry thatoperates as: a transmitter that, in each of the transmission events,selects the first group and causes each transducer element in the firstgroup to transmit ultrasound focusing at a predetermined depth in thesubject, the first group in one transmission event differing inposition, in the transducer element array direction, from the firstgroup in a previous transmission event by a shift amount correspondingto at least twice a width of a single transducer element in thetransducer element array direction; a receiver that selects at leastsome transducer elements among the plurality of transducer elements ofthe ultrasound probe, and generates a receive signal sequence for eachof the at least some transducer elements based on ultrasound reflectionreceived by the transducer element; a delay-and-sum calculator that, foreach of the transmission events: sets a target area including aplurality of measurement points, the target area at least including anarea where the ultrasound transmitted from the first group in thetransmission event focuses in the subject, wherein at the predetermineddepth, a width of the target area in the transducer element arraydirection is equal to or greater than the shift amount; and generates asub-frame acoustic line signal composed of a plurality of acoustic linesignals, one for each measurement point included in the target area, byperforming, for each measurement point that is included in the targetarea, delay-and-sum processing with respect to one or more receivesignal sequences corresponding to the measurement point, the one or morereceive signal sequences corresponding to the measurement pointrespectively generated for one or more transducer elements composing asecond group of transducer elements, among the plurality of transducerelements of the ultrasound probe, based on ultrasound reflectionreceived from the measurement point; and a synthesizer that generates aframe acoustic line signal based on a plurality of sub-frame acousticline signals corresponding one-to-one with the transmission events.

This structure prevents the occurrence of defective areas in ultrasoundimages when combining the synthetic aperture method with conventionaltransmission beam forming, and thus enables increasing frame ratewithout image quality degradation.

(2) In the ultrasound signal processing device of (1), for each of thetransmission events, the delay-and-sum calculator may set, as the targetarea, a combination of: a first area having an hourglass shape, having abase corresponding in position to the first group in the transmissionevent, and having minimum width in the transducer element arraydirection at the predetermined depth, the minimum width being smallerthan the shift amount; and a second area adjacent to the first area inthe transducer element array direction at least at and around thepredetermined depth.

This structure provides an enlarged target area whose width in thetransducer element array direction is equal to or greater than the shiftamount, by including a first area that covers an area in whichtransmitted ultrasound is in-phase and a second area that covers anoutside of the area in which transmitted ultrasound is in-phase.

(3) In the ultrasound signal processing device of (2), for eachmeasurement point, the delay-and-sum calculator may perform thedelay-and-sum processing by using delay amounts for the respectivetransducer elements composing the second group, a delay amount for agiven one of the transducer elements composing the second group beingbased on a total propagation time being a total of a transmission timebeing a time amount required for transmitted ultrasound to arrive at themeasurement point and a receive time being a time amount required forultrasound reflection from the measurement point to arrive at thetransducer element.

This structure enables a sub-frame acoustic line signal to be generatedby performing delay-and-sum processing for each measurement point in thetarget area.

(4) In the ultrasound signal processing device of (3), for eachmeasurement point included in the first area, the delay-and-sumcalculator may use, as the transmission time, a first arrival time thatis calculated by using a first time amount and a second time amount andthat changes depending upon a depth of the measurement point, the firsttime amount being a time amount required for transmitted ultrasound toarrive at a reference point included in the first area and at thepredetermined depth, the second time amount being a time amount requiredfor transmitted ultrasound to arrive at the measurement point from thereference point, and for each measurement point included in the firstarea and deeper than the predetermined depth, the first arrival time maybe calculated by summing the first time amount and the second timeamount, and for each measurement point included in the first area andshallower than the predetermined depth, the first arrival time may becalculated by subtracting the second time amount from the first timeamount.

This structure enables a sub-frame acoustic line signal to be generatedby performing delay-and-sum processing for each measurement point in thefirst area by calculating a transmission time based on a distance from atransmission focal point.

(5) In the ultrasound signal processing device of (4), for eachmeasurement point included in the second area, the delay-and-sumcalculator may use the first arrival time as the transmission time, andfor each measurement point included in the second area and deeper thanthe predetermined depth, the first arrival time may be calculated bysumming the first time amount and the second time amount, and for eachmeasurement point included in the second area and shallower than thepredetermined depth, the first arrival time may be calculated bysubtracting the second time amount from the first time amount.

This structure enables a sub-frame acoustic line signal to be generatedby performing delay-and-sum processing for each measurement point in thesecond area by calculating a transmission time based on a distance froma transmission focal point.

(6) In the ultrasound signal processing device of (4), for at least eachmeasurement point at the predetermined depth, among a plurality ofmeasurements included in the second area, the delay-and-sum calculatormay use, as the transmission time, a time amount required fortransmitted ultrasound to travel though any path from a transducerelement of the first group to a point at the same depth as themeasurement point.

This structure avoids discontinuity in the change of transmission timesfor measurement points in the second area, which would otherwise occurdue to a distance between measurement points at the transmission focaldepth and the transmission focal point, and improves ultrasound imagequality.

(7) In the ultrasound signal processing device of (6), for each of themeasurement points included in the second area, the delay-and-sumcalculator may use, as the transmission time, a time amount required fortransmitted ultrasound to travel through a path from a transducerelement of the first group that is located at a center position of thefirst group in the transducer element array direction to the measurementpoint.

This structure enables calculating transmission times for measurementpoints in the second area according to a method that does not dependupon the transmission focal point.

(8) In the ultrasound signal processing device of (6), among measurementpoints in the second area that are located along each of at least oneline perpendicular to the transducer element array direction, for eachboundary point located in a periphery of a boundary between the firstand second areas, the delay-and-sum calculator may use the first arrivaltime as the transmission time, wherein for a boundary point deeper thanthe predetermined depth, the first arrival time may be calculated bysumming the first time amount and the second time amount, and for aboundary point shallower than the predetermined depth, the first arrivaltime may be calculated by subtracting the second time amount from thefirst time amount, for an intermediate point being one of themeasurement points that is located at the predetermined depth, thedelay-and-sum calculator may use, as the transmission time, a secondarrival time being a time amount required for transmitted ultrasound totravel though any path from a transducer element of the first group to apoint at the same depth as the intermediate point, and for a pluralityof measurement point between the boundary point and the intermediatepoint, the delay-and-sum calculator may set respective transmissiontimes so that the transmission times monotonically increase asmeasurement point depth increases, without any discontinuity between thetransmission times.

This structure ensures that, for measurement points in the target areathat are located along a straight line perpendicular to the transducerelement array direction, transmission time monotonically increaseswithout discontinuity as depth increases. Thus, this structure improvesultrasound image quality pertaining to the second area and a boundarybetween the first area and the second area.

(9) In the ultrasound signal processing device of (8), for each of themeasurement points included in the second area, the delay-and-sumcalculator may set the transmission time according to T_(M)=αT₁+(1−α)T₂where T_(M) denotes the transmission time for the measurement point, T₁denotes the first arrival time, and T₂ denotes the second arrival time,and where variable α=0 for the intermediate point, α=1 for the boundarypoint, and a increases without discontinuity as a difference betweenmeasurement point depth and the predetermined depth increases.

This structure ensures, with a simple method, calculating transmissiontimes for measurement points in the target area that are located along astraight line perpendicular to the transducer element array direction sothat transmission time monotonically increases without discontinuity asdepth increases.

(10) In the ultrasound signal processing device of (2), for twoconsecutive transmission events, the delay-and-sum calculator may settwo target areas respectively corresponding to the two consecutivetransmission events so that the second areas of the two target areaspartially overlap one another in the transducer element array direction.

This structure ensures a maximum overlap count of at least two withinthe second area, and thus improves ultrasound image quality pertainingto the second area.

(11) In the ultrasound signal processing device of (10), the secondareas of the two target areas respectively corresponding to the twoconsecutive transmission events may overlap one another by at least 50%in terms of area.

This structure ensures an overlap count of at least two within at least50% of each second area, and thus improves ultrasound image qualitypertaining to second areas.

(12) In the ultrasound signal processing device of (2), thedelay-and-sum calculator may generate a sub-frame acoustic line signalfor the first area and a sub-frame acoustic line signal for the secondarea, and the synthesizer may combine a plurality of sub-frame acousticline signals for the first area that correspond one-to-one with thetransmission events to generate a first combined acoustic line signal,and combine a plurality of sub-frame acoustic line signals for thesecond area that correspond one-to-one with the transmission events togenerate a second combined acoustic line signal, and generate the frameacoustic line signal by combining the first combined acoustic linesignal and the second combined acoustic line signal.

This structure avoids the first area and the second area from affectingone another in terms of image quality, and thus improves ultrasoundimage quality.

(13) In the ultrasound signal processing device of (1), the ultrasoundsignal processing circuitry may further operate as: an amplifier thatamplifies each sub-frame acoustic line signal by using amplificationfactors corresponding one-to-one with the measurement points included inthe target area, an amplification factor for a given measurement pointdetermined based on the number of signals combined to generate theacoustic line signal for the measurement point.

This structure avoids a difference in overlap count between measurementpoints from affecting image quality, and thus improves ultrasound imagequality.

(14) Another aspect of the present disclosure is an ultrasound signalprocessing device: performing a plurality of transmission events eachinvolving selecting a first group of transducer elements from among aplurality of transducer elements of a ultrasound probe that are arrangedin at least one line along a transducer element array direction, andcausing each transducer element in the first group to transmitultrasound towards a subject; for each of the transmission events,generating a sub-frame acoustic line signal based on ultrasoundreflection received from the subject in response to the transmissionevent, to yield a plurality of sub-frame acoustic line signals eachcorresponding to a different one of the transmission events; andgenerating a frame acoustic line signal based on the sub-frame acousticline signals for the transmission events. The ultrasound signalprocessing device includes ultrasound signal processing circuitry thatoperates as: a transmitter that, in each of the transmission events,selects the first group and causes each transducer element in the firstgroup to transmit ultrasound focusing at a predetermined depth in thesubject, the first group shifting in the transducer element arraydirection from one transmission event to another; a receiver thatselects at least some transducer elements among the plurality oftransducer elements of the ultrasound probe, and generates a receivesignal sequence for each of the at least some transducer elements basedon ultrasound reflection received by the transducer element; adelay-and-sum calculator that, for each of the transmission events: setsa target area including a plurality of measurement points, the targetarea at least including an area where the ultrasound transmitted fromthe first group in the transmission event focuses in the subject,wherein at the predetermined depth, a width of the target area in thetransducer element array direction greater than a width of a singletransducer element in the transducer element array direction; andgenerates a sub-frame acoustic line signal composed of a plurality ofacoustic line signals, one for each measurement point included in thetarget area, by performing, for each measurement point that is includedin the target area, delay-and-sum processing with respect to one or morereceive signal sequences corresponding to the measurement point, the oneor more receive signal sequences corresponding to the measurement pointrespectively generated for one or more transducer elements composing asecond group of transducer elements, among the plurality of transducerelements of the ultrasound probe, based on ultrasound reflectionreceived from the measurement point; and a synthesizer that generates aframe acoustic line signal based on a plurality of sub-frame acousticline signals corresponding one-to-one with the transmission events.

This structure improves image quality at areas in ultrasound imageswhere two consecutive transmission events overlap, even when the shiftamount is set to a width of a single transducer element.

(15) Another aspect of the present disclosure is an ultrasounddiagnostic device including the ultrasound signal processing device of(1). In the ultrasound diagnostic device, the ultrasound signalprocessing device may be configured so that the ultrasound probe isconnectable thereto.

This structure achieves an ultrasound diagnostic device having theabove-described features.

Although the technology pertaining to the present disclosure has beenfully described by way of examples with reference to the accompanyingdrawings, it is to be noted that various changes and modifications willbe apparent to those skilled in the art. Therefore, unless such changesand modifications depart from the scope of the present disclosure, theyshould be construed as being included therein.

What is claimed is:
 1. An ultrasound diagnostic device comprising: anultrasound probe including transducer elements; and an ultrasounddiagnostic circuit that functions as: a transmitter performing anultrasound transmission event of causing a transmission transducerelement array composed of all or some of the transducer elements totransmit ultrasound; a receiver generating reception signal sequences,one for each of the transducer elements of a reception transducerelement array composed of all or some of the transducer elements, eachof the reception signal sequences generated according to a signal basedon reflected ultrasound that a corresponding one of the transducerelements receives in response to the transmission of the ultrasound; adelay amount generator generating delay amounts, one for each of thetransducer elements of the reception transducer element array; and adelay processor performing delay processing on the reception signalsequences, based on the delay amounts, wherein the delay amountgenerator includes: a transmission time generator generating only once,for a measurement point within an area of reach of the ultrasound of theultrasound transmission event, a transmission time that is a time periodfrom transmission of the ultrasound until arrival of the ultrasound atthe measurement point; and a reception time generator generatingreception times, one for each of the transducer elements in thereception transducer element array, the reception times each being atime period from reflection of the ultrasound at the measurement pointuntil arrival of the ultrasound at the transducer element, wherein thedelay amount generator generates the delay amounts based on thetransmission time and the reception times, and the transmission timegenerator, when distance from a transmission reference point to themeasurement point is greater than distance from the transmissionreference point to a focal point, generates the transmission time basedon a sum of time for transmitted ultrasound to arrive at the focal pointfrom the transmission reference point and time for transmittedultrasound to arrive at the measurement point from the focal point, andwhen distance from the transmission reference point to the measurementpoint is smaller than distance from the transmission reference point tothe focal point, generates the transmission time based on subtractingtime for transmitted ultrasound to arrive at the measurement point fromthe focal point from time for transmitted ultrasound to arrive at thefocal point from the transmission reference point.
 2. An ultrasounddiagnostic device comprising: an ultrasound probe including transducerelements; and an ultrasound diagnostic circuit that functions as: atransmitter performing an ultrasound transmission event of causing atransmission transducer element array composed of all or some of thetransducer elements to transmit ultrasound; a receiver generatingreception signal sequences, one for each of the transducer elements of areception transducer element array composed of all or some of thetransducer elements, each of the reception signal sequences generatedaccording to a signal based on reflected ultrasound that a correspondingone of the transducer elements receives in response to the transmissionof the ultrasound; a delay amount generator generating delay amounts,one for each of the transducer elements of the reception transducerelement array; and a delay processor performing delay processing on thereception signal sequences, based on the delay amounts, wherein thedelay amount generator includes: a transmission time generatorgenerating only once, for a measurement point within an area of reach ofthe ultrasound of the ultrasound transmission event, a transmission timethat is a time period from transmission of the ultrasound until arrivalof the ultrasound at the measurement point; and a reception timegenerator generating reception times, one for each of the transducerelements in the reception transducer element array, the reception timeseach being a time period from reflection of the ultrasound at themeasurement point until arrival of the ultrasound at the transducerelement, wherein the delay amount generator generates the delay amountsbased on the transmission time and the reception times, and thetransmission time generator, when the measurement point is farther fromthe transmission transducer element array than a focal point is,generates the transmission time based on a sum of time for transmittedultrasound to arrive at the focal point from the transmission referencepoint and time for transmitted ultrasound to arrive at the measurementpoint from the focal point, and when the measurement point is closer tothe transmission transducer element array than the focal point is,generates the transmission time based on subtracting time fortransmitted ultrasound to arrive at the measurement point from the focalpoint from time for transmitted ultrasound to arrive at the focal pointfrom the transmission reference point.
 3. The ultrasound diagnosticdevice of claim 1, wherein the delay processor identifies, for eachtransducer element of the reception transducer element array, areception signal value corresponding to a delay amount from thereception signal sequences, and generates an acoustic line signal forthe measurement point based on the reception signal values identified.4. The ultrasound diagnostic device of claim 3, wherein the transmissionevent is performed a plurality of times, the transmission time generatorgenerates the transmission time to the measurement point only once foreach transmission event, and the delay processor generates an acousticline signal for the measurement point, based on the reception signalsequences for each of the transducer elements of the receptiontransducer element array of each transmission event.
 5. The ultrasounddiagnostic device of claim 1, wherein the reception time generatorgenerates the reception times based on distances between the measurementpoint and the transducer elements of the reception transducer elementarray.
 6. The ultrasound diagnostic device of claim 1, wherein the delayamount generator generates the delay amounts for each of the transducerelements of the reception transducer element array by adding thetransmission time to the reception times for each of the transducerelements of the reception transducer element array.
 7. The ultrasounddiagnostic device of claim 1, wherein the receiver generates thereception signal sequences according to signals based on reflectedultrasound that the transducer elements receive from inside a subject inresponse to the transmission of the ultrasound, and the measurementpoint is set inside the subject.
 8. An ultrasound diagnostic methodcomprising: performing an ultrasound transmission event of causing atransmission transducer element array composed of all or some transducerelements of an ultrasound probe to transmit ultrasound; generatingreception signal sequences, one for each of the transducer elements of areception transducer element array composed of all or some of thetransducer elements, each of the reception signal sequences generatedaccording to a signal based on reflected ultrasound that a correspondingone of the transducer elements receives in response to the transmissionof the ultrasound; generating delay amounts, one for each of thetransducer elements of the reception transducer element array; andperforming delay processing on the reception signal sequences, based onthe delay amounts, wherein the delay amount generating includes:generating only once, for a measurement point within an assumed area ofreach of the ultrasound of the ultrasound transmission event, atransmission time that is a time period from transmission of theultrasound until arrival of the ultrasound at the measurement point; andgenerating reception times, one for each of the transducer elements inthe reception transducer element array, the reception times each being atime period from reflection of the ultrasound at the measurement pointuntil arrival of the ultrasound at the transducer element, wherein thedelay amount generating generates the delay amounts based on thetransmission time and the reception times, and the transmission timegenerating, when distance from a transmission reference point to themeasurement point is greater than distance from the transmissionreference point to a focal point, generates the transmission time basedon a sum of time for transmitted ultrasound to arrive at the focal pointfrom the transmission reference point and time for transmittedultrasound to arrive at the measurement point from the focal point, andwhen distance from the transmission reference point to the measurementpoint is smaller than distance from the transmission reference point tothe focal point, generates the transmission time based on subtractingtime for transmitted ultrasound to arrive at the measurement point fromthe focal point from time for transmitted ultrasound to arrive at thefocal point from the transmission reference point.
 9. An ultrasounddiagnostic method comprising: performing an ultrasound transmissionevent of causing a transmission transducer element array composed of allor some transducer elements of an ultrasound probe to transmitultrasound; generating reception signal sequences, one for each of thetransducer elements of a reception transducer element array composed ofall or some of the transducer elements, each of the reception signalsequences generated according to a signal based on reflected ultrasoundthat a corresponding one of the transducer elements receives in responseto the transmission of the ultrasound; generating delay amounts, one foreach of the transducer elements of the reception transducer elementarray; and performing delay processing on the reception signalsequences, based on the delay amounts, wherein the delay amountgenerating includes: generating only once, for a measurement pointwithin an assumed area of reach of the ultrasound of the ultrasoundtransmission event, a transmission time that is a time period fromtransmission of the ultrasound until arrival of the ultrasound at themeasurement point; and generating reception times, one for each of thetransducer elements in the reception transducer element array, thereception times each being a time period from reflection of theultrasound at the measurement point until arrival of the ultrasound atthe transducer element, wherein the delay amount generating generatesthe delay amounts based on the transmission time and the receptiontimes, and the transmission time generating, when the measurement pointis farther from the transmission transducer element array than a focalpoint is, generates the transmission time based on a sum of time fortransmitted ultrasound to arrive at the focal point from thetransmission reference point and time for transmitted ultrasound toarrive at the measurement point from the focal point, and when themeasurement point is closer to the transmission transducer element arraythan the focal point is, generates the transmission time based onsubtracting time for transmitted ultrasound to arrive at the measurementpoint from the focal point from time for transmitted ultrasound toarrive at the focal point from the transmission reference point.
 10. Theultrasound diagnostic method of claim 8, wherein in the delayprocessing, for each transducer element of the reception transducerelement array, a reception signal value corresponding to a delay amountis identified from the reception signal sequences, and an acoustic linesignal for the measurement point is generated based on the receptionsignal values identified.
 11. The ultrasound diagnostic method of claim10, wherein the transmission event is performed a plurality of times,the transmission time generating generates the transmission time to themeasurement point only once for each transmission event, and the delayprocessing generates an acoustic line signal for the measurement point,based on the reception signal sequences for each of the transducerelements of the reception transducer element array of each transmissionevent.
 12. The ultrasound diagnostic method of claim 8, wherein thereception time generating generates the reception times based ondistances between the measurement point and the transducer elements ofthe reception transducer element array.
 13. The ultrasound diagnosticmethod of claim 8, wherein the delay amount generating generates thedelay amounts for each of the transducer elements of the receptiontransducer element array by adding the transmission time to thereception times for each of the transducer elements of the receptiontransducer element array.
 14. The ultrasound diagnostic method of claim8, wherein the reception signal sequences are generated according tosignals based on reflected ultrasound that the transducer elementsreceive from inside a subject in response to the transmission of theultrasound, and the measurement point is set inside the subject.